Periodically, I need to refer folks to good resources for ramping up on WPF 3D functionality. Here are the ones I commonly refer to:
Mike Hodnick has a great, succinct WPF 3D tutorial, which is an excellent resource to get up and running with the technology. If there is any one tutorial to try- I would say go there.
Charles Petzold has helped countless Windows UI developers ramp up on the technologies - his 3D book blog has a lot of good insights for developers, without making heavy assumptions about a reader's 3D theory knowledge as other resources sometimes do. He has a lot of interesting nuggets on his 3D book blog, often demonstrating the power of XAML, as well as a 3D samples page. As he is a frequent contributor to MSDN magazine, I periodically encounter his articles introducing users to technology like the MeshGeometry3D type which can be quite helpful.
The 3D Team blog and Daniel Lehenbauer's blog are more topical resources, with references to a lot of cool new applications, or addressing common questions.
The 3D tools package isn't a tutorial per-se, but a library of goodies for use with WPF, by the 3D team. Any serious WPF 3D developer should be aware of the cool offerings in this package.
Depending on your application domain, you may want to see this "casual" game developer's tutorial for WPF3D - "Creating 3D Webgames using ATMO NQAL 2.0". The tilt on this series of tutorials is quite distinctive, and delves into quite a bit of application details. Definitely different from your typical WPF/3D tutorial :)
WPF Unleashed - Adam Nathan brought in Daniel Lehenbauer (3D dev team lead for V1 WPF) to prepare the 3D chapter in this title. An excellent ramp up to 3D.
3D Programming for Windows - Charles Petzold's new book on WPF 3D is now available. I haven't had a chance to get my hands on this one yet, but based on his blog and prior writings, you can expect a detailed coverage of the subject.