Hosting Silverlight in a SharePoint Webpart by Kirk Allen is an excellent step-by-step guidance for combining Silverlight and SharePoint.
Check out the Telerik's Silverlight TreeView Load on Demand example that demonstrates "best practice" for using RadTreeView with load on demand and ADO.NET Data Service. The source code is also available here.
Mike Snow with new helpful tip - How to Dynamically Load a Silverlight Control within another Silverlight Control.
Silverlight 2 Gotcha - Tab Navigation in a Popup - Jeff Handley noticed that Tab key doesn't work for moving from one control to another. He also found a solution for this issue!
Laurence Moroney explains how to deal with the Silverlight plug-in versions installed on client's machines in the first few days after RTW to ensure a smooth migration from Beta 2 to the final.
Flash vs Silverlight: Recursion Tree - another cool example made by Terence on Flash and Silverlight.