Starglider Systems Blog
Hidden WPF: Secrets for Creating Great Applications in WPF by Alessandro Del Sole covers some less know things in WPF.
While there are a few non-obvious items, if you read something like WPF 4.5 Unleashed you are unlikely to learn something now.
Might be worth checking out in Safari, as it is quite short. Most examples are in VB, though.
WPF MVVM In Depth is a PluralSight course by Brian Noyes that covers using the MVVM pattern (Model/View/ViewModel pattern) in WPF.
I really like the way MVVM cleanly separates concerns. Great for re-usability and unit testing. It also goes pretty nice with WPF.
I have taken some of Brian Noyes courses before, and as usual this one was pretty clear and had very useful examples to follow along.
Overall, very much recommend if you are interested in MVVM in WPF.