AudioSurf - Whenever I get a batch of new music, an AudioSurf session won't be far behind--and then I always find myself playing previous favorites, as well.
Fallout 3 & Fallout New Vegas: Exceptional games with so much content that you can play different ways. The last time I played Fallout NV, I went straight evil and wiped out the first town, including a few quest-givers. Also, Old World Blues, my favorite DLC ever, is fantastic to play over. It's like being in an episode of Dr. Who. On top of that, mods. Mods are awesome.
Final Fantasy Tactics - My most played game ever. Love the combat and the challenge of getting everything. LOVE Deep Dungeon.
Bloodrayne & Bloodrayne 2 - Shut up.
Might & Magic: Clash of Heroes - I really like the battles. The story and characters are good, as well.
Also, Scrabble, Chess, and World of Goo.
