Those who have worked in depth with WPF know what a valuable tool Snoop is. It allows you to see the visual tree of a WPF application, change values, track events and much more! Just the other day I was thinking how good it would be if we had a 'Snoop for Silverlight'.
I recently discovered Silverlight Spy, which does just that. You can snoop into the visual tree of any Silverlight 2 application. Before you install it, make sure you have installed the pre-requisites, escpecially the web browser control that it needs to stream the web content.