I've decided to go through my XBLA games and finally try to get some of those pesky co-op achievements. A lot of them aren't even difficult, they just require two or more people. So, if you'd like to help (or need help) getting them, just post here. I'm willing to help others even if I already have them. Off the top of my head, here are some games I have with co-op achievements I'd like to get done:

R-type Dimensions

Schizoid

1942: Joint Strike

WOTB: Commando 3

Castle Crashers