Rogue Trader

Rogue Trader is a Future Warhammer game system that is also a campaign setting. Its an extension of Dark Heresy, but you don't need any knowledge of it to have a good Rogue Trader campaign. The core rulebook is pretty much all that you need for your first campaign, so if you decide that you don't like it you only spent like 20 bucks. This book is pretty thick, so I actually recommend getting a hard copy. Like with most of the games I play, I also recommend using fillable character sheets, as they make bookkeeping a lot smoother if you're all sitting around on your laptops.
Character Options include the standard d20 future classes such as soldier, gunner, and navigator, as well as some interesting new classes concerning The Void (outer space), where most of your adventure will be taking place. The core book doesn't give any rules for races other than humans, but the included rules on gruesome mutations and cybernetics leave room for plenty of character customization.
Look into Rogue Trader if your group has a heavy focus on role playing and likes a future setting with a darker atmosphere.