I've created a Windows Presentation Foundation Tools and Controls page that has a permanent link in the left navigation bar. Whenever I hear of a new tool or control that helps designers or developers create WPF applications, I'll add it to the list. If you're aware of any that I've missed, please send me an e-mail that includes a one- or two-sentence description and a link. The tools and controls that I link to need to be downloadable (directly or by request) or available for purchase.
Activity in the WPF space continues to increase, and I expect this list to grow quickly in the coming months.