Xbox Live Arcade Game

[MikeSobe]

Castle Crashers is a lot of fun to play with friends.

As has been mentioned
Trials HD if you're a masochist (it's a fun game but very frustrating at times which only makes it that much more rewarding when you pass a level)
Geometry Wars (2)
Uno

 

[Man Called X]

If anyone is down for Castle Crashers, I'm always up to play it. I freaking love that game.