Yakuzaice on 06 December 2008
Warhawk. I know it's been mentioned plenty of times, but it is my favorite multiplayer game this gen next to TF2 (PC). Even if I'm not that good at it lol.
I also rather enjoy MGO, but it seems to be a love it or hate it game.
Outside of shooters, LBP and Wipeout HD are fun.