PC:
Counter Strike: Source - Lol, most obvious.
Team Fortress 2: Very fun and I love the graphics and game play. I play it all the time now for some reason.
StarCraft Original/BroodWar: Of course STARCRAFT! Wonderful game, the first PC game I've ever played and STILL play.
MapleStory: Well yeah, it's just fun. I play it to stay in contact with my family, who all plays MapleStory.
Need For Speed: Carbon: Well, I LOVE cars. And racing.
Call Of Duty 2 Single/Multiplayer: I think one of the best WW2 games out there.
PS2:
Dynasty Warriors 5: Empires: Yeah I still gotta finish the game, love the series.
Resident Evil 4: Okay, I beat almost every mode for the game, but it's still fun breaking someone's neck
Dance Dance Revolution: Hey, very fun, keeps you in fit.
Wii:
Wii Sports: Amazing...
Super Smash Bros Brawl: I love this game for the WII!