What are some good on-line co-op games?

What games do you enjoy playing in on-line co-op? From FPS to sports games what have you really enjoyed? I'm currently playing Golf with Friends and enjoying the simple, sometimes relaxing, sometimes frustrating nature of the game.

Parents
  • One of my favorites has to be call of duty! 

Reply
  • One of my favorites has to be call of duty! 

Children
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