One of our designers has started a new blog that focuses on Avalon from a designer's perspective. I've seen some of the demos he's worked on internally, and they're very impressive. As someone who works so close to the technology, I'd expect some great content to be posted here in the future. He already has a good article on non-traditional button design that's worth a look. Great job, Nathan.
While I'm at it, I noticed that the Xamlon guys are hosting a XAMLBlogs.com site that aggregates other XAML-related content. Check it out.