I already have Halo, Call of Duty and Rock Band. Looking for some games to play with friends. A lot of multiplayer games are only one or two players per console.
Here are some 360 games that allow 4 player on the same console. It's another site with a list that allows you to sort. I've linked to the sorted page already. There are also reviews which specifically focus on co-op attributes of the games.
I'm nice, so I made a list of the replies so far with 4 player local support.
Aegis Wing
Bomberman LIVE
Call of Duty
Castle Crashers
Feeding Frenzy 2
Gauntlet (XBLA)
Geometry Wars 2
Halo
Marvel Ultimate Alliance
Monster Madness
N+
NBA 2k9
Rainbow Six Vegas 2
Rock Band
Scene It?
Splosion Man
TMNT: Turtles in Time Reshelled
Worms 1/2
I downloaded Gauntlet, but since it's the port of the arcade version and nothing like the previous console versions, it's not very fun since the original arcade game existed only to eat up all your quarters.