Looking for a good Co-op player game (free)

yoshimtux

I am looking for a good co-op game for me and my friend. Please do not post a game that is simulliar to WoW since there is so many games like that out there, I'm sure it would cross a couple of your minds. We are looking for something unique and preferred not a cartoonish game, as far as shooter / hack and slash / or any other type of game, they are all fine.