Oh, I can't forget about Warhawk! I have no idea if you're into shooters at all, but Warhawk is fantastic. It may be a bit late to join the community as only the hardcore players are left, but definitely look out for a sequel (hopefully it's coming).
I'm personally a huge fan of both Resistance games, though I know many people on here hate on them far too much. I think they're worth a shot, but it'd probably be best to rent if you aren't sure. (the reason why I love R2 is for the co-op which I highly recommend).
EDIT: I'm not able to use my PS3 right now (I'm at college and it's at home...), but if you add me on the PSN, I'll be home some weekends and I can get on to play some online games (I have both Resistance games, Killzone2, LBP, WipEout HD, and Warhawk). My PSN ID is aceninja007. 