I play all my VALVe game on 1680x1050 with all settings on high and at least 2x AA and 4x AF. I get about 60-120 frames per second depending on which game and where I am in the game (I tend to get better frames in Counter-Strike Source in comparison to Day of Defeat: Source).
There are some games which are just time fillers, like Football Manager, or Pool that sort of thing, however games like Day of Defeat just needs to played as big as possible, on a monitor as huge as possible with the sound turned up way loud...
Valve Games: High Res 1440 X 900 with detail fairly high up...
WoW: Windowed but Maximized because up until recently it allowed for faster alt-tabing because I use the web alot while playing to find locations for stuff....
Almost all other games besides WoW: Full screen...
plus now for the first time I have a dedicated Vid card...so I cant alt-tab almost anything!!! woo!