Let me throw one or two odd ones in...
1.) Diaspora - It's based on the FATE system, which means it can get quite metagamy, but, as I discovered recently is a lot of fun to play. Especially because you and your buddies get to design your own universe at the beginning. Don't worry, the process shouldn't take longer than one session.
2.) Ashen Stars - I haven't played but it is based on the Gumshoe system which I really, really like. It's more investigation based, so this might be a little problem
and for fun:
3.) 3:16 - A little Indy game that you can use for a few evenings in between. Basically it's "shoot the alien, conquer the planet, R&R, repeat ad nauseam" ;D