I'm sure the vast majority of you people already know the card game Uno. A few weeks ago Microsoft announced that a Xbox Live Arcade version of this classic game will soon be available, and it's now playable on the Debug version of Xbox Live. Here is a video, showing the different game modes and how it's played. Surprisingly fun and well done.
Update 2: Uno is now officially on XBLA, so the video is back again.