Chris Anderson, an architect on the WPF team at Microsoft, wrote Essential Windows Presentation Foundation, which has just hit the bookstores.
WPF is as much a philosophical shift from other UI technologies (WinForms etc) as it is a technical shift. Consequently, understanding both aspects is important to being a profficient WPF developer. Chris draws on his architectural experience with WPF to provide a book with a solid foundation of technical exposition and many code samples. Interwoven with this is the the philosophy of WPF, a story that includes discussion of WPF design decisions, WPF V.Intended vs WPF V.Actual, and both understanding and applying key WPF programming principles. From this perspective, Chris's book is unique with respect to the other main WPF books, which include:
* Programming Windows Presentation Foundation, by Ian Griffiths and Chris Sells (soon to be re-released with comprehensive updates)* Windows Presentation Foundation Unleashed, by Adam Nathan* Applications = Code + Markup: A Guide to the Microsoft Windows Presentation Foundation, by Charles Petzold