In my head everyone in the universe has at least one Xbox 360, if not two. I know several people with more than one system. I had two for awhile. It's hard for me to imagine that there is someone that doesn't own one. Not you. You don't count, Sony fanboy.
If there is one, Amazon.com has a really great deal. If you buy a 4GB Xbox 360 console you'll get a $50 Amazon promotional credit to buy something else with. Maybe your original Xbox 360 is being assy and you need to replace it. This would be a way to get a new system and a game!
There's a similar deal for the Kinect sensor. Buy it and you'll get a $25 credit towards something else nice at Amazon.com.
Note that both of these are limited deals. In either case you'll see your account credited within two days.