What are some good multiplayer games for xbox 360?

Me and two other people always play together on xbox live. We want a multiplayer game that needs teamwork and cooperation to play. Or anything like GTA IV multiplayer where you can just run around in cars and kill people. Any multiplayer RPGs would be great. The Best picks would be either Shooter (1st or 3rd person), Action, Free-Roam/Sandbox games, or an RPG. We're open to any suggestions :)