One of my favourite tools to help me with WPF at the moment is Snoop (http://blois.us/Snoop/). It's really handy to do some visual debugging of WPF at runtime. It allows you to explore the visual tree of you application, and all it's associated properties.
I found it useful to debug what resources I'm actually using as well as where and/or what elements I've used to make up the screen.
The 3d View is very cool. It allows you to see an exploded view of the UI and how it's put together and you can rotate it to get a better view.
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