Gears of War, Mass Effect, Bioshock, Assassin’s Creed, Forza 2, Halo 3, Burnout 3. Army of Two just came out this week and is really fun co-op. But, you can have the same kind of fun in Gears of War, and Gears has been out for a while so you can score it on the cheap. Mass Effect, Bioshock and Assassin’s Creed are single player only, so if you’re looking for more multiplayer stuff, stick to the other titles.