Planets

Exact number of planets in the Galaxy is unknown. They are 300-350 billions of stars, that have from zero to fifteen (if only planets are counted) or around a two hundred (if all moons are counted as well). This gives a lot of space for the empires to wage their neverending wars (not to mention a lot to fight for), even if you exclude the systems lying too far from the discovered hyperlanes to use them in any way.
Planets were more or less categorized, as a part of the so called Orlik-Hunchman scale created during the times of the Solar Commonwealth. From five types of stellar bodies, four describe various types of planets and other stellar bodies that aren't stars. There are not only many planets, but also many types of them.

Type 2 Stellar bodies

Objects that are simply impossible to be colonized or terraformed due to their natural characteristics. They can be inhabited, especially when there are important resources that warrant exploitation. But all colonies will be temporary, made to be abandoned when they are no longer needed.

Type 2a - Giants

Gas Giant - Giant planets that are made mostly of various gasses surrounding a relatively small core. Many of them are used to 'mine' useful gasses (depends on their exact composition). Their strong gravity means that they often have many moons. Their usefulness depends almost solely on their composition, with as many of them being of immense value as there are gas giants that noone is realy interested about. Jupiter and Saturn are an example of Gas Giants.
Ice Giant - A giant planet composed of heavier matter than a Gas Giant, often frozen form of water. Almost always on outer reaches of star systems. Of relatively low value to average economies, though they often have some moons and can serve as a decent source of said 'heavier matter' for outposts on them. Majority of them has very little worth to any country.

Type 2b - Others

Carbon Asteroid - Asteroid composed mostly of carbon. Quite useful source of it when there are no Carbon Planets around to dig for it. Most of asteroids are of this category.
Silicon Asteroid - Asteroid composed mostly of silicon and chemical compounds with it. Rarer than carbon ones and, ironically, tends to be of smaller value.
Metallic Asteroid - Asteroid composed mostly of various metallic particles and compounds. Quite valuable but unfortunately rare. Still, when they exist, they are often mined for resources.
Aberrant Asteroid - All asteroids whose composition fits neither of the aforementioned categoris. They are relatively rare and often very valuable, depending on what type of matter actually builts them. Sometimes they can be very weird, especially when the system has some marks of past existence of a weird species.
Comet - Stellar object composed in most cases of ice, methane, solid carbon dioxide and ammonia. Unless one of them is urgently required, they are often left alone to wander star systems, if only for aesthethic sense.
Dwarf Planet - Object too small to become a proper planet but too big to remain an asteroid, with its gravity strong enough to flatten its surface into ball-like form. This category includes those of the dwarf planets that didn't receive a World Forge treatment due to possessing a number of extremely features that made nanoterraformation impossible. This means that they are all barren and lifeless, due to lack of atmosphere and weak gravity. The most extensive human habitation they might possess are typically some mines or research labs.

Type 3 Stellar bodies

Planets that are unable to sustain life (sometimes with exception of a protozoans), but their terraformation is at least theoretically possible. But simply too costly and requires a great technological prowess. Pluton and most of Jupiter and Saturn moons are of this category.

Type 3a - Natural Planets

Frozen Planet - A planet that exists on the far fringes of its solar system, that can be described as something similar to Solar System's Pluto. Terrifyingly costly to terraform in any way, and commonly inhabited merely on a scale of few mining stations or research installations (even if they accidentally blew out a planet, nothing of value is lost alongside it). Despite everything, some of the less extreme Frozen Planets were terraformed.
Infernal Planet - A planet that exists much too close to its star, pretty much like Solar System's Venus or Mercury. Terrifyingly costly to terraform in any way, and commonly inhabited merely on a scale of few mining stations or research installations (even if they accidentally blew out a planet, nothing of value is lost alongside it). Once again, some of them were terraformed during the golden age of the Solar Commonwealth.
Barren Planet - A planet that simply does not possess an atmosphere, or a very shallow one. It is a simple, lifeless rock, in most cases devoid of magnetic field. Trying to terraform it into something meaningful is possible, but the costs (and required technologies) of achieving make it rather unfeasible at least since the Mankind lost the access to the World Forge. Pre-terraformation Mars can be an example of a Barren Planet. Luna can be an example of a Barren Moon.
Carbon Planet - A rare cousin of Barren Planet that is different because it is constructed mostly from carbon rather than silicon. This makes it a treasure trove for any respectable star nation that simply love turning them into Mining Worlds. A single one can supply entire star sector in carbon required for producing various types of plastics (and things like graphene as well). If one mines deeper one can find carbides or even diamonds in great amount counted in millions of tonnes. Despite this, they are absolutely toxic and, while theoretically possible, rather pointless when it comes to terraformation.
Iron Planet - A planet that lost its entire mantle (due to powerful impact or being bathed in fires of the local star) and now remains as a ball of iron and other heavy elements. Sometimes called Cannonball Planet. Once again, theoretically they could be terraformed, but it's almost utterly pointless as they are much better stripmined for resources. They are, however, rather rare and often simply ignored (unless the demand for heavy elements in the area is big).
Volcanic Planet - Planet torn by extreme volcanic activity, with very dense atmosphere built mostly from carbon dioxide. In most cases also with liquid, metalic core which means both gravity (often... substantial) and magnetic field. They are quite often colonized but never terraformed since the loss of World Forge. They offer almost infinite amount of cheap geotermal energy, the air that is already so toxic that you can just throw all the waste away without care for ecology, and a lot of resources quite closely. They make for a good industrial planets, especially when there are nearby planets that can be used to supply it with food.

Typer 3b - Antropogenic Planets

Junkyard Planet - Someone (one of many past alien species most likely) used this planet as a massive garbage dump for reasons unknown (they are easier ways of disposing of your waste. Effects are rather grim. Landscapes filled with long rusted junk and various machinery that no longer works (many of them already broken to the point of being little more than metallic sediment), but sometimes entire starships can be found. Some of them even with archeotechs.
Weirdly enough, most of the Junkyard Planets seems to once be a Type 5 planets. They used to have a working biosphere, before someone ruined everything. Now it's toxic wasteland, cleaning of which might take centuries. That again, recycling is possible and there are many possibilities for science.
Shattered Planet - Once a Type 5 planet with extensive biosphere and, most likely, a sapient inhabitants. Now it is a sad remainder of fate that befells species that fail to built a galactic empires of their own and are visited too early to defend themselves. Whoever was the attacker, he used relativistic weaponry to literally rip the entire planet into pieces. Now it's broken ruin, with exposed core (its gravity keeps the remnants together and prevents them from changing into an asteroid belt). It can be exploited (as an archeological site and so on), but it can't be terraformed without an application of utterly nonsensical ammount of resources.

Typer 3c - Archeoplanets

Ethereal Planet - Contrary to popular opinion Ethereal Planets do not exist. Or, to be exact, they exist only visually. Whatever happened to this place when it was swallowed by the Hyperspace, it caused its cessation of existence while making it remnants exist as sort of immaterial form. The planet can be seen (including all the little details of its surface), but it can be safely flown through. It simply doesn't exist. And, thus, cannot be terraformed or inhabited.
Hyperspace Planet - Planet that doesn't exist on our dimensional plane, but in Hyperspace. It is a form of a proto-archeoplanet, that will be overtime changed into one of other archeoplanets. For now, it exists as a sort of middle form. It is a permanent wound in Reality that allows ships to enter Hyperspace in the middle of the system, one that also has gravity and magnetic field that is detectable in Realspace (and they can have both natural and artificial sattelites in Reality). On the other hand, it is also a treasure trove of archeotechs. Even if also a deadly place, with mortality and insanity rates quite high amongst those that dare to enter it.
Ghost Planet - It is unknown what exactly happened to it while it was in the Hyperspace, but whatever it was it wasn't pretty. It was at least partially converted into one of the Ghosts. It seems at least partially not of this world, and has a tendency for occasional phasing back and forth, which tends to be fatal for everything living upon it. Thus they look like Barren Planets in most cases. Unusable for anything beside research, and even this from safe distance.
A-Entropic Planet - Another weird type of archeoplanet. This one emerged from the Hyperspace at least partially broken. The entropy around it seems heavily disturbed and in most cases simply doesn't work. This on first glance absolutely great thing is mostly ruined by the fact that all sapient species that exist on it feel a profound sense of wrongness and, if left for too long, probably will go insane. Still, a prime research material. In most cases Barren Planets, since their unique characteristics are a major trouble for evolution to occur.

Type 4 Stellar bodies

Planets possible to colonize and terraform, but ones that still requires the latter for humans to be able to live easily on them. Even without them life is quite easy, as at least some of the things (atmosphere, magnetic field and so on) required to unrestrained habitation is there, even if it still requires adjustments. Mars could be a good example of this category.

Type 4a - Natural Planets

Toxic Planet - A planet that for some reason is extremely toxic to humans and similar species. The reasons for that can include extreme ammounts of heavy metals, long abandoned nanotechnology, microbes that see chlorophyle as its enemy and murder every sort of plant that the colonizers might try to introduce. Some of them include a thriving biosphere, that simply adapted to local environment or evolved in it. Some of them are a barren wastelands. All of them however have to possess at least some atmosphere, which means that terraforming is at least possible.
Dead Planet - A planet that exists in a 'green belt' surrounding the star, when temperature is actually quite good for a development of life... that however doesn't possess it. Some of them are Barren Planets with rudimentary atmosphere, others have signs that suggest that they used to be inhabited before something sterilized them. Despite this, most of them are possible to colonize, even if they are devoid of atmosphere they are still at the perfect part of the system where no 'thermal' terraforming is needed which lowers the associated troubles (and costs) at least a bit. They became astronomically rare in the inhabited area of space due to them being a prime target for World Forge application.
Arctic Planet - Some worlds on the outer edges of the Solar Systems were stabilized by the World Forge nanites (due to a combination of factors that are barely understood) in the form of a world whose amplitude of temperature ranges from few Celsius degrees below 0 to just slightly above zero. There are also similar worlds encountered 'naturally', being essentially worlds on the outer edge of the Green Belt.
Arid Planet - Arid Planets are a common name for planets that are too hot for a lot of water to exist there... but with either atmosphere or a temperature only a bit too high for humans. In both cases terraformation requires mostly adding water and relatively minor thermal engineering, which makes them a common target for terraformation and colonization, if discovered in post-World Forge era.

Type 4b - Antropogenic Planets

Fortified Planet - A planet that used to be a Fortress World of some extremely militant and now long gone species. One can discover fortified lines many thousand kilometres long, thousand bunkers capable of surviving anything short of tactical nuke, underground storage halls with automatic (and mostly broken but reparable) lines sending fuel, ammunition and provisions to said bunkers... if one searches deep enough, one can find ancient command rooms and fallout shelters.
The problem? Things like that are everywhere and are a severe detriment to any construction plans, plus such planets are mostly sterile but almost always have breathable atmosphere. This is explained by the theory that they were created by some sort of automatic drones that went insane, at least judging from almost schizophrenic level of their architect's paranoia. Most of them requires quite extensive terraformation which includes introduction of an ecosystem and dismantling of 95% of preexisting constructions which changes a planetwide schizophrenic maze of long abandoned bunkres into a natural fortress.
Graveyard Planet - A grim reminder of the deadliness of Space. Once a thriving Type 5 planet with extensive biosphere and a sapient species inhabiting it. Now? A graveyard. They are many internal types, some suffering still dangerous level of fallout (remaining after a nuclear war that killed all but most determined lifeforms), while the rest seems... different. At least half of them is an utter mystery to scientists. While grim, they can be terraformed.
Battlefield Planet - Planets like that are often found near hyperspace anomalies, which leads to some suggestions that they might in fact be archeoplanets, habitable planets swallowed by Hyperspace and there subjected to either increasing madness of its inhabitants or some extradimensional invasion. They are a battlefields left after ancient wars that led to deaths of all higher lifeforms. In most cases devastation is profound, with most of the planet scorched by nuclear fire or poisoned by gas weapons, not to mention being flattened by sometimes even a century long artillery fire.
Dyson Planet - A long abandoned smaller variant of Dyson Sphere. That for some reason lacks the star inside. This makes its usage rather hard, unless one invests a lot of money for basic infrastructure. That again, the ability to host population is almost boundless (and entire insides can be used to built things). The material used to construct it is superdense making bombardment pretty much useless and forcing the attackers for a gruelling battle for attrition.
Many of them are colonized as important and well secured ship construction locations, due to their particular nature.

Type 4c - Archeoplanets

Klein-Mobius Planet - Archeoplanet with the space surrounding it "looped" towards the insides. Its orbit cannot be left, as the faster ship tries to fly away, the faster he soon flies towards it. Landing on it is extremely dangerous as well, as one can suddenly discover that the spatial pocket he entered is smaller than his ship.
Each Klein-Mobius Planet has a single safe route that allows to go in and out. Localizing it however is a feat achievable only by strongest civilizations around. Nation that achieves it gains a natural fortress, since all ships that try to enter it have to follow the same exact route. On the other hand, it is a detriment to trade and makes all orbital installations simply impossible.
Cursed Planet - Planet that seems... broken. In a way. It is most certainly a type of Archeoplanet, and one that the Hyperspace wasn't merciful for. Leaving confines of domes and vehicles tends to be dangerous, with even survery teams reporting missing members, mental disorders and "alien" thoughts. In one particular case, a sattelite showed a dismembered corpse of a scientist lying in the middle of the camp, with other scientists casually working around it... and then reporting not seeing anything. And with their equipment proving they were right. Very rare and, in fact, many doubt their existence.
Time Displaced Planet - Planet where time was broken during its brief visit in Hyperspace. According to the skies visible from there, most of them seems to be temporary 'late' than Galaxy at large, with Supernovas whose explosion should be visible dozens of years ago still looking like normal stars. What's more, time itself seems distorted there, sometimes running faster and sometimes slower. A prime research place, but one that is otherwise hard to colonize. Curiously, all of them seem to have a biosphere, however rudimentary it was.

Type 5 Stellar bodies

Planets possible to be colonized from the start, or terraformed to fit the needs of the organic life. Obviously rare (aside from Human Space-part colonized during the Diaspora), and of great strategic and economic value. Earth is an example of Type 5a planet.

Type 5a - Natural Planets

Terran Planet - A planet that is more or less Earth-like. Natural ones are extremely rare, most of them is actually an aftermath of extensive terraformation programs during the Diaspora, with local fauna hailing from Earth and in worst cases modified to fit planet better. Prime colonization target.
Super-Terran Planet - A planet that is more or less Earth-like... but bigger. Up to ten times bigger. It is a term however that is used to describe only planets with Terran-like biosphere, which gets rarer the higher in size one goes due to gravity. They are rare and in most cases require low amount of heavy metals or some ancient archeotech terraforming device. Immensely valuable.
Ocean Planet - In majority of cases, a former Ice Giants that were pushed towards their star and managed to stabilize themselves in a habitable zone. Very, very rare. And with oceans that can be hundreds of kilometres deep. Biosphere can be introduced to outer parts of it, which together with floating artifical isles allows them to be colonized.

Type 5b - Antropogenic Planets

Machine Planet - Aftermath of the Virus that decimated the Berserks at the height of their expansion. Created by one of more... 'alien' divergent groups of the Berserks. At first glance a Terran planet with expansive biosphere. But when one looks closer, one can discover that there is next to no life. Plants and animals alike are in fact machines, with expansive use of nanotechnology to simulate their growth and the entire proces of eating each other. Colonizable, if one introduces their own crops.
Paradise Planet - Sometimes called Type 6 planet. A world created by extensive process similar to terraformation but much more advanced. Calm climate, weather and tectonics, 100% of plants and animals edible and in most cases delicious, a lot of natural crops and many trees give fruits. Plus eternally clear air (cleaned by archeotech nanites), plus entire landscapes sculpted to be beautiful. Seemed to be created by beings of similar aesthetics and biology to humans, probably some elusive prehuman group. Extremely rare and valuable.
Dark Planet - A world on the very edge of the Solar System, without enough light to maintain plantlife - but terraformed with the World Forge. Their air is breathable, but the surface has very limited biosphere, and it's night is permanent. Typically of very limited human habitation.
Magic Planet - World created as a playground of some ancient species of immense technological prowess, but that is not sure. Mostly due to it not leaving any clues to its origin. Terran World with pico and femtomachines in the air that can be used to do things normally impossible (like conjuring fire from thin air) that are often referred to as 'magic'. Plus a lot of uniquely sculpted resources that can be found only on them. Unfortunate side effect is that there are many murderous beasts that were probably created to be faced with such magic. Very rare and very valuable.

Type 5c - Archeoplanets

Citadel Planet - A relatively small planet rebuilt into a tool of war. It can be described as a dwarf planet-wide sea of nanites whose self-repair ability is used to protect its internal machine from even the strongest bombardment. It has an armament, either a Graser EW or a Magnetic Acceleration Weaponry of truly epic proportions. A single Citadel Planet can destroy fleets while being essentially indestructible (their weak point is a control room floating atop the see of nanites, though it repairs itself after a while if destroyed). Considered an archeoplanet because found in Hyperspace, it is believed that someone tossed them there for a purpose. But what purpose?
Clockwork Planet - A machine copy of a planet. One or two kilometres beneath the surface (one rocky, with metal ores and so on) a machines begin, going all the way into the core. One that are beyond comprehension of modern civilizations. They are responsive for the magnetic field, atmosphere and so on, essentially being the ones to make the world live. They also serve as essentially limitless energy source, if one manages to tap into their vast potential.
Living Planet - A rather weird archeoplanet. One that lives. It is filled with archeotech nanites that serve as its internal organs, including brain and underground 'cables' that serve as nervous system. There is a consciousness as well, but it's hard to understand and impossible to communicate. Curiously, such planets are in most cases alive, with many animals exhibiting weird and sometimes unnervingly intelligent behaviour.