When Silverlight 3 launched, we also published several additional application themes for the navigation and business application (for .NET RIA Services) templates. I just uploaded two more themes from one of our designers, Corrina, to the Expression Gallery. There are versions for both navigation application template as well as the .NET RIA Services business application template.
Additionally, several fixes were made to the existing templates that some users reported. I also added .NET RIA Services templates for those that were missing based on requests (Retro, Skyline, Subdued).
I noticed also that others have been uploading themes, behaviors and other goodness to the Expression Gallery, so be sure to check it out!