A new Windows Mobile development book has just been released by Andy Wigley, Daniel Moth and Peter Foot called Mobile Development Handbook. I had a chance to read a few of the chapters and it's one of the best books out there for mobile development using Compact Framework and is targeted from the beginner to the advance developer. They cover things from GUI development to Security to Interop and even have a chapter on .NET Compact Framework 3.5 and Visual Studio 2008 (Orcas) from a device developer perspective. Whether you are just starting mobile development or have been doing it for a while this is definitely a book that is needed on the shelf :)