Some of you may already be aware of this little tool but just thought I would share it with those who are not aware of its existence:
XAMLPAD MSDN Doc
Its a little program that allows you to test rendering XAML code and view the Visual Tree of your XAML code easily. I wont go into all of the features as they are mentioned in the doc linked to above.
Perhaps worth adding to the "WPF Tutorials & FAQs" thread or something, I dunno ?