As a developer for Windows Phone 7, Microsoft provides great design guidelines for building your applications. Even with that, it is often difficult to translate the guidelines into actual consistent code. The team at expression blend saw the need and came up with an excellent solution. From the Inside Windows Phone show (Their video has better audio/video sync)
The design templates are XAML-based templates for building Windows Phone Applications. These templates make it possible for you to copy paste XAML to easily create common Windows Phone UI layouts, and since the templates follow the Windows, you get a â€œmetroâ€ experience with zero effort.
You can download the XAML here but it is not available at the moment. I hope in time they add more controls like mapping and such in the future. I think the resource will be great for building great looking apps that match the overall interface because the developers will have more time with working on the content and and design instead of worrying about often used controls.