As time goes by I keep finding more and more great WPF applications, but this one really got my attention. The Audi Keyboard is a WPF application that was designed for UMPCs that was used during the Melbourne Motorshow to input customer data. I actually found it on the Hugo Ortega's Uber Tablet blog (which I'm huge fan by now) so it might have been missed by pure .NET geeks. Hugo published video with overview of this project where you can learn more details.
This project is great example of how WPF brings together designers and developers enabling them to work together on the same project. There is also very interesting video interview up on ScreenEdit.com with Richard Bassett (the designer) and Dr. Neil (the programmer). As they point out the most important lesson they learned is that with WPF each of them can work in the environment they are comfortable with (designer = Expression Blend, developer = Visual Studio), but this would be still part of the same project (remember that Blend reads and creates .csproj files). Also worth noting are the first impressions of seasoned designer coming to the Expression suite, and comparing it to competitive technologies like Flash and Adobe Illustrator.
After working with WPF for a while I can 100% agree with what they say.