XAML Power Toys is a Visual Studio 2008 SP1 Add-In that empowers WPF developers while working in the XAML editor.
The add-in installation package, source code and instruction videos can be downloaded here: http://karlshifflett.wordpress.com/xaml-power-toys/
David
Karl has uploaded PowerToys with Silverlight support. It's very cool. I've written a quick walkthrough for creating a LOB app using XAML Power Toys, MoXAML and Silverlight. You can see it here.