Learning WCF: A Hands-on Guide by Michele Leroux Bustamante
A good beginners guide to WCF.
Programming WCF Services by Juval Lowy
Explains the architectural aspects of WCF and how it was engineered.
Essential Windows Communication Foundation (WCF): For .NET Framework 3.5 by Steve Resnick, Richard Crane, Chris Bowen
Good guide to the changes introduced by Visual Studio 2008 and .NET 3.5
Inside Windows Communication Foundation by Justin Smith
This is a great reference to WCF internals. Advanced programmers only.