Did you ever see a Silverlight application and wonder "how did they do that?"
With Silverlight Spy, it's easy to peek into the code, both the logic and the XAML, to learn how other people built their applications.
Now, it's been updated to work with Silverlight 2 beta 1, so you can take a look into Silverlight 2 projects.
Be sure to read the FAQ about the pre-requisites for installing the app, namely the csEXWB control.