The Xbox with Kinect
is on sale at Amazon right now for only $299.99. Plus, scroll down to Special Offers, you will find the $100 Amazon credit and follow 'click here' to add the item to cart.
Here is the detail of the $100 credit:
"Add to Cart From This Page to Get a $100 Amazon.com Credit with the Purchase of the Xbox 360 4GB Console with Kinect. For a limited time, buy the Xbox 360 4GB Console with Kinect from the "add to cart" button below and receive a $100 Amazon.com credit good toward the purchase of items shipped and sold by Amazon.com"