Shank, EA and Klei’s just-dated downloadable PSN and XBLA side-scroller, has a cooperative mode. Not quite sure if that was already public information, but it’s got it. And EA’s released the trailer above to prove they’re not pulling anyone’s legs.
This is a bit of a good news / bad news situation though; the co-op mode consists of a prequel “mission,” singular, and is only playable locally. Which really is a bummer.