Silverlight Spy is awesome!

Silverlight Spy is awesome! I'm a huge fan of FireBug for debugging web applications. Silverlight Spy is basically the same thing for Silverlight apps. The free version lets you inspect any Silverlight app. The paid version lets you change properties of objects on the fly and see the changes right on the screen. I'm in UI debug heaven. It does more things too. I haven't tried the advanced features yet, like the Event and Performance monitors.