Big Screen Headlines MCML Application
Ok this is one of the best Media Center Markup Language application I have seen so far.
Its an RSS reader for Media Center written in MCML for Vista. You can browse the feed setup by Niall Ginsbourg (the developer) or add your own feeds using IE7. It plays enclosed videos and audio files.
Niaill has made good use of MCML, and I hear more is on the way from Niall too