Hoping that Killing Floor goes cheap, so I can get a 3rd copy for when my younger brother visits, that's a good game to kill some time.
I recently got Binding of Isaac, that's a great little game, totally unique, and funny, and pretty damn addictive. It's not frustrating either, even with no continues or saving - just try and do your best, to kill your mom... what more do you need!
I got about halfway through Grimrock, and it started to kinda get on my nerves - I think that the puzzles are far too samey, it's a pretty repetitive, claustraphobic game - but it is good, don't get me wrong. I think that the problem is I keep expecting more, more variation, more weapons, enemy types, and it's dawning on me that it's probably shown me all it has. Hoping that a sequel will have more content, and less step-combination-puzzle-fuckery.
Ohh, and it would be lovely if ARMA2 would drop it's price a bit - been meaning to try that DayZ mod, but I can't justify paying £26 just to play a mod, with all the youtube coverage, you'd think they'd try and encourage some fresh sales.