Good online game?

I'm looking for a good online game besides Call of Duty 4 for PS3. I have a 100 Wal-Mart gift card and would like to purchase 2 online games. Suggestions would be greatly appreciated.

Oh, I would also like to know what a good headset is for the PS3. Thanks in advance.

unreal tournament(if u want) and warhawk!!(must buy)

for me at least :P