Multi-player games?

Hey just wondering what kind of online multiplayer games you guys play? I think it would be way cool to find some team games to play and create some teams from this board.

I don't get into anything too dark/evil (i.e. Quake etc)... but if there is one that people really like, I'd be willing to buy it - or better yet, maybe theres a free game online somewhere that kicks butt.

What do you guys think - anyone interested?