There aren't many Silverlight pages on the Web yet, but I've just stumbled into http://www.microsoft.com/uk/students which uses Silverlight to seduce students.
Other amusing demos include the page turner (below) and Fox's movie taster, where the video quality is the most impressive part.
I notice that Microsoft's Michael Scherotter is also implementing the ribbon user interface in Office 2007 for use on a Web site.
IMicrosoft has been showing off a jigsaw demo, which is amazing. It's like an ordinary on-screen jigsaw except that instead of being a chopped up still picture, it's a movie. You can move the pieces around, and yes, there's part of the movie running on each individual piece.
Someone who knows could post a link to it in comments. And anybody who reckons they can do the same thing in a browser window using Flash, Java, Python, APL, BBC Basic or whatever is welcome to post a rival demo. I'll be even more impressed.