A few months ago I blogged about Metro-styling a WPF application. My post merely scratched the surface and never considered styling any other controls besides the main window, but now guys that brought you XAML Spy have open sourced a library for building Modern UI style WPF applications. You can check out the code over at codeplex repository. It is really easy to get started, simply use the following NuGet command:
And with only a few changes you will transform your basic looking window from this:
Check out their web for more information over at codeplex.
If you are really into using Metro in your classic WPF applications, another option MahApps.Metro. The above window will be restyled to look like: