I'm a fan of Enemy Territory games. The newest one (Quake Wars) was pretty fun. And it was different.
Grid is a awesome game, you won't be dissapointed in that.
Call of Duty MW and WaW were are both fun.
Spore is a good way to kill time, if you don't mind DRM.
I'm in the middle of Far Cry 2 right now, and it's okay IMO. It has really good moments, and really dull ones.
Again, Team Fortress 2 online is soooooo much fun. It takes a little bit to get use to, but it's well worth it IMO.
Fallout 3 is ok.
I've heard good things about STALKER: clear sky, but I've never played it.
Also Grand Theft Auto series is a great way to kill time.