The crux of the following post is this: Prince of Persia Classic is on sale for 400 ($5) this week. There are some other things on sale as well, but you don't really need to know about them. You can just proceed directly to the bottom of this post and follow the Xbox Live Marketplace link to Prince of Persia Classic.
Okay fine, if you really want to know what the other deals are, here we go. First, you can pick up some Transformers 2 DLC for 400 ($5). Second, Watchmen: The End is Nigh is available for 800 ($10) instead of the usual, ridiculous 1600 ($20). There. Happy? Now go buy Prince of Persia Classic.
Xbox.com: Add Prince of Persia Classic to your Xbox 360 download queue ($5)
Xbox.com: Add Transformers 2 Character and Map Pack Plus to your Xbox 360 download queue ($5)
Xbox.com: Add Watchmen: The End is Nigh to your Xbox 360 download queue ($10)