I play first-person shooters and recently upgraded my computer. I don't have a lot of spare time, but I might be able to join in occasionally.
My old system wouldn't play Battlefield 1942 very well, but this system should. I haven't installed it yet and would be a complete n00b, but hey, it's about fun, right? (I'm still putting together my new system. The final step will be an overclock, I think.)
The last game I played online extensively was Wolfenstein: Enemy Territory. I haven't played that in awhile, though.
Everyone has at least probably tried Counter-Strike, right? I didn't play it very much because of the rampant cheating. I was a n00b anyway and didn't appreciate script kiddies invading the game with speed and headshot hacks. Worse are subtle cheaters. I never knew if I really sucked that badly or if others were cheating.
(God, I love the emoticons on this site...very cute!)