Mine would have to be Halo 2. We used to get a bunch of us together and system link with a few beers. It was friggin sweet. Honourable mention would definitely be the original Gears of War and Smash Bros Melee on GameCube. Oh and GTA liberty city stories. We used to play that in school when it came out. There was a gametype where each team had to capture the others limo. That was awesome too.