Wow, Microsoft is going to be putting content from SDCC up on Xbox Live for download. I don't know what all will be available, but here is the page for brief info:

http://www.xbox.com/en-US/community/eve ... efault.htm

So far, the content is more game and media related. But they did put up the Superman Doomsday trailer

http://www.xbox.com/en-US/community/eve ... ticker.htm

Also, they have some themes up for a small price:

http://www.xbox.com/en-US/live/marketpl ... themes.htm