Actual settings or "just" regional source books? I always thought it would be nice to use their d6 system (especially in the current incarnations) for other games. It is flexible and it doesn't use the strange dice other games use.
At least from according to the title the upcoming books will be more general ones.
Feral Cities, Ghost Cartels, Runners Companion, Unwired, Street Magic.
I'm keen to hear about all the systems mentioned, not only those that I listed.

This has been a great thread so far!
Pinotage
Ars Magica:
You normally play a wizard in a real world medieval setting. The wizards are very secretive and neutral because of the fear that if they help one group all the other groups will turn against them. They are more or less in conflict with the church as faith and magic cancel each other out.
The magic system in Ars Magica is very freeform as spells can be build on the fly, meaning a mage can do everything if his skill is high enough.
Vampire:
You play a vampire in the current time an a quite organized shadow society living alongside the normal world. Each city is ruled by a lord (usually a very old vampire) and every vampire in this city must follow his orders. The usual enemies are other vampires who draw too much attention, vampires who think that they should rule the world instead of living alongside humans in the shadows, werewolves, vampire hunters or other supernatural predators.
As Vampire is part of the World of Darkness its easily possible to play as one of the other factions (werewolves, vampire hunters, etc.) in the same setting
Warhammer Fantasy:
I don't know much about the RPG but I think a basic understanding of the setting makes it easier to explain Dark Heresy.
Warhammer is a standard Fantasy world, meaning it has Orcs, elves and dwarves but it is much more conflict ridden than the usual D&D world. Around the north pole a portal into the Warp has opened (Think something like Hell) and from there the corrupting influence of chaos (and magic) spreads over the world. Its influence twists everything it touches into insane and mutated cultist who make pacts with demons and summon their minions. Much of the rest of the world tries to stop it or at least hold it of as long as they can as it is more or less established that in the end chaos will win (in a few hundred years or so).
The nations opposing the chaos barbarians are two human nations, one inspired heavily by renaissance Germany and the other by medieval france and the typical elves (magical and haughty) and dwarves (living in mountains etc.).
There are also some other forces in the world like Orcs who are at war with everyone and live only for battle, a horde of undead lead by vampires and a jungle nation of lizardmen which are the main factor which keeps chaos at bay because of their strong magic.
Because of the corrupting influence of Chaos everyone is always on the lookout for heretics (demon worshippers).
Dark Heresy (WH40K):
Warhammer 40K is basically the Warhammer Fantasy setting transplanted 40.000 years into the future. Mankind has conquered nearly the whole galaxy and is the dominating force, but has fallen into "technological barbarism" where machines are seen as being inhabitant by spirits which have to be soothed by ritual anointing to keep the machine working.
The Emporer, a immortal human which lead the mankind to greatness is dead, but his body is kept alive by his golden throne and 1000 sacrifices each day as he powers a device which makes it possible for navigators to travel through the Warp (only form of FTL travel and remember, Warp = Hell). The human empire is so huge that governing it is nearly impossible and messages may take decades or even centuries before they reach Holy Terra.
The society resembles a Gothic one. Many structures and ships are look very Gothic and important names are in Latin. Because of the Chaos everyone who does not believe in the Emporer as God, or keeps relations with aliens or mutants is killed by the inquisition. Two quotes from the WH40K PC game "Kill the alien, the mutant, the heretic" and "A open mind is like a fortress with its gates unlocked".
You see, its not a nice place. Because there are so many humans in the world the live of individuals don't matter much except when they are exceptional individuals. Each day million soldiers die and millions more are recruited from thousands of Hive worlds.
The elite soldiers of mankind are Space Marines, genetically modified humans who constantly fight against the creatures of Chaos (or worse, Space Marines turned traitors), Eldar (Space elves with their own mysterious agenda), Orcs (Living Bioweapons whos only purpose is to fight no matter whom), Necrons (Living machines bend on harvesting all souls from the universe), Tau (A highly advanced upstart race) and the Tyranids (Extragalactic monsters sharing a hive mind and harvesting whole planets fro biomatter).
In the RPG you don't play Space Marines but normal humans which have been recruited by a Inquisitor to be his retinue. Your job is to hunt chaos worshippers and otherwise fulfil missions for the inquisition. The standard setting is in a relative peaceful sector of the galaxy which has a Dark Prophecy about destruction.
GURPS
Gurps has no formal setting. Instead it is a general roleplaying system. That means no matter what you want to roleplay with GURPS, be it space adventures, high magic fantasy, low (or no) magic history, current time spy setting, etc. you can. Its very modular and many of its setting books can be used as inspiration for games with other systems
DSA
DSA (Das Schwarze Auge. Engl: The Black Eye. The PC games are known as "Realms of Arkania" outside Germany) is a German RPG (probably the most played RPG inside germany, surpassing D&D on the regional market) and not very well known outside Germany. It is a low/mid magic fantasy RPG playing in the world "Aventurien". The world is more gritty than most D&D setting but not as gritty as Warhammer. It generally pays a big attention to details and captures the mediveal feel of the world very well.
Rifts:
Rifts is a very original setting which allows for nearly anything.
The setting background is the same as in Shadowrun. In the future magic returned to the world, but with more catastrophical consequences. Magic is fueled by people dieing and releasing their psionic energy. And when there was a limited nuclear exchange between two countries enough people died for magic to become active again.
The resulting magical backlash killed more people which resulted in stronger magical backlashes and so on. In the end most humans were dead and the civilization was destroyed. The few humans that survived started to rebuild society. The problem was that the magic also opened many portal to other universes and because of the high magic levels earth became interesting for a lot of being living there which migrated to earth.Those being range from "humans from other dimensions" to "truck sized one eyed tentacle monsters".
The societies in the world range from farming communities ruled by warlords (humans or otherwise), big magical kingdoms (Camelot), beacons of advanced societies (Germany), fascist regimes (US East Coast), inter-dimensional trade hubs (Atlantis) and monster filled wilderness (everything else). Because of earths status as dimensional nexus you can find and play nearly anything be it normal humans of various occupations, dragons, lizardmen, fey, borg like cybermen, etc. And if it does not exist, just create it. There is nothing which does not fit into the world somewhere.
The problem with this system are the rules. The organization and formatting of the books is bad. To create a character you constantly have to go forth and back in the book to look at the all the tables. Also the balancing is way off. For example when creating a character you can create a Glitterboy Pilot (Glitterboy = Mech with enough firepower to level a skyscraper with one shot) which includes the mech or a vagabound scout with only a kevlar west, binoculars and a 9mm handgun. When playing the scout you have to be very careful as there are two types of damages in this game. Normal damage (SDC) done by things like handguns and mega damage (MDC) done by cruise missiles, lasers, etc. When you only have armour against SDC weapons then you are dead after being hit by a single point of MDC damage. Likewise you can't really harm someone wearing MDC armour with a SDC weapon. ANd as quite a lot of things in Rifts have MDC weapon and armour (even foot soldiers) playing someone who does not have MDC weapons and armour is not a good idea.