Professional Sql Server 2005 CLR Programming - Highly Recommended
I was walking through Barnes & Noble last week and I came across this book from Wiley. I bought it to see what Derek and Doug had to say. I've read a bunch of pieces of this book and it is very informative. They discuss the technical aspects of development and they cover a lot of the whys of doing things, such as TSql vs CLR, along with performance. If you are working in the Sql Server 2005 area and are looking at Sql Server CLR objects, you need this book. It is highly recommended!
PS. I write for Wiley, but I spent good money on this book on my own.