"The Noun Project" is a new and upcoming graphics design initiative to make a lot of Windows Phone 7 designers and developers. The project collects, organizes and adds to the highly recognizable library of symbols of free pictograms/icons for common nouns and concepts that make up the universal visual language, which also happens to be a major theme in Microsoft's Metro design style. The best part, all icons are guaranteed to be free.
Still in it's early stages, the website currently offers a solid set of 500+ icons. Unfortunately searching and categories are still being developed so it makes finding icons somewhat difficult in the meantime, but nevertheless fun to browse. They also plan to accept third-party contributions and host competitions to continue growing their collection.
More Info: The Noun Project