Professional Microsoft SmartPhone Programming
I just got a copy of Professional Microsoft SmartPhone Programming and all I can say is NICE! I always worried that the first real SmartPhone book would not go into enough depth to be useful. Not an issue here. Basically, the book is a list of "What would you like to do with Smartphone" and shows you how to do it.
I need to finish reading the last two chapters before I can fully review it but having read most of it already, this book is just plain good and if you have any interest in Smartphone Programming, it's worth its weight in gold.