What are some fun co-op games?

Halo 3, Halo Reach, Call of Duty Modern Warfare 2, Call of Duty Black ops, Gears of War 2, Marvel Ultimate Alliance, Fable 2 (Sort of you play as almost a Hench man, well one guy does), Baldur's Gate: Dark Alliance 1 and 2, Mass Effect, Champions of Norath 1 and 2, Borderlands. Hope I helped XD