New Media Center application - TVTonic MCE
TVTonic have made available a Media Center version of their application. Installing it lets you watch four channels they stream over the web - News, MoviePick, Cartoon Cow and Rawdio. Once installed it's available in More Programs inside Media Center like any other application. It's pretty cool, I've got the MoviePick channel running in the office right now - there's a trailer for The Alamo on right now and interviews with the cast.
The one complaint I have is that they appear to host the video themselves and don't actually use Media Center for playback, so you can't pause or stop the content.