http://expression.microsoft.com/

The Expression Community for designers and developers creating rich, modern interactive user experiences across web, desktop, and phone.

http://www.microsoft.com/design/toolbox/

.toolbox is a fun online learning environment, where you will learn basic design concepts and how to apply them, as well as the fundamentals of creating Silverlight applications using the Expression Studio tools. .toolbox features two learning options: Courses and Tutorials.

http://www.expressionblendstepbystep.com/

The companion web site for Expression Blend 4 Step by Step