I haven't played many games in quite a while, but I try to play Civilization III whenever I can. I'm not much for RPGs, which means I have a lot more time than most of my friends
Civ III and SimCity 3k are the only single-player games I like to play, but I play StarCraft when a few of my friends are on b.net, and CounterStrike and UT when I feel like mindless killing for a while.