A hard sci-fi campaign taking place in something highly derivative of Kim Stanley Robinson's Mars series. It'll probably be something like Blue Mars in terms of actual year, technology, as so forth. All humans, but many would be from lower-gravity places than earth, and there would be extensive use of 'designer genes', making for very, very long lifespans (like in the books), and plenty of strange features.
My main campaign idea involves a scientist 'cracking' the puzzle of empty-space energy, and the ensuing chaos caused by the fight for the solution for 'unlimited' energy. It would also assume (unlike the Mars series) that quantum technology had come into use, so there would likely be AI (because of quantum computing), very flaky matter-transportation (good for sending raw materials like metals, bad for anything complex), technically correct methods for time travel (but requiring faaaar too much energy to actually try), and instantaneous communication over unlimited distances (so long as you can get entangled matter to the 'other end').
So, with empty-space energy, all sorts of things become possible; quick interplanetary travel, short (~5 year) trips to the next star, limited time travel, high-powered beam-weapons, 'creation' of matter, and so on. This would, of course, cause horrible things to happen to the status quo, so 'the man' wants to keep empty-space energy 'down'. The PC 'races' would consist of terrans (who would be standard humans, unless you didn't want all the other races to have a STR penalty, in which case they'd have a STR and CON bonus from the lack of exposure to low gravity and radiation), martians (fairly tall, skinny guys), and non-planetary people (reeeeeally tall, skinny guys).
The campaign will likely involve a lot of stuff on mars (since that's where the scientist who solves empty-space energy works), likely including exploring a semi-terraformed surface where you can go indefinately without any gear at the low altitudes if you've got the right genes, and there's liquid water on the northern hemisphere, but non-locals (and the otherwise unadapted) have trouble going much higher than the low points, and strange, bio-engineered creatures may, or may not be running amok.
Oh yeah, and there's space elevators.