RTCW MP - Still have not found a game that can touch this for its multiplayer clan games.
1/ Return to Castle Wolfenstein - Got this game at the same as getting broadband and got absolutely hooked. The class based multiplayer has ruined any other type of online fps for me. This game is the sole reason I did **** in college but I still love it anyway.
2. - RtCW
RTCW my first online fps game and wow....it wasnt so much the standard 7min rounds that were so good but the 45min beach map or other custom maps with no time limit.....you could end up having a 7hour battle just refusing to go bed and let the other team win as you never felt they deserved the victory.
RTCW