Chaos faction 2 is one of the best 2 player games SMO arena fighter is also good game, addicting Light temple i think is the name ( new game ) is ment to be 1player playing 2 characters at once, but it's good for 2 player
Tanks is a two player game that i used to play with my little brother. I certainly enjoyed it but the only downside is that it's not on this site. (bummer)