What is the best book on Silverlight 4?

Silverlight/Expression 4 Books!I recently stumbled upon a post asking, “What is the best book on Silverlight 4?” In the age of the internet, it can be hard for anyone searching for a good book to actually find it. I have read a few Silverlight 4/Expression books in 2010 and decided to post the “best of” collection. Instead of reading multiple books, you can cut your list down to whatever category