You can also explore the features of XAML Power Toys. This will give you a extended power to design your XAML. This is really a good AddIn not only for the designers but also for the developers. You can create your ViewModel class, create ListView or Form for selected class, extract properties to style, option to generate x:Name for controls, grouping controls inside GroupBox and lots of other goodies. Check out the site for the latest features.
Mole is a tool that integrates with Visual Studio which lets you inspect the Visual Tree of your application, view and edit properties or data, view the XAML for selected elements and more. It allows unlimited drilling to objects and sub objects.
Snoop is a tool which you can use to hook to your running WPF application and browse the Visual Tree of the application. You can also inspect and edit the properties, inspect routed events and magnify sections in the UI and also debug binding errors.
Crack.Net is a runtime debugging tool for .Net desktop applications (both WPF & WinForms) just like Mole & Snoop. It allows you to go thru the managed heap of another .Net application, view all kinds of values on different objects and also manipulate them easily. You can also read the Crack.Net article.