Windows Icons
This Modern UI Icons project was started back in October 2011 with the goal of allowing developers a single solution for icons. Licensed under Creative Commons 3.0 the pack has grown very rapidly with hundreds of suggestions through Twitter.
Thank you all so much for all the support and suggestions. If you found these useful feel free to donate me a beer.
Windows Phone 
Currently there are hundreds of 76x76 icons provided in this pack. Both XAML and SVG vector files are provided and I encourage you to use them instead of static PNG files wherever possible. Be sure to only use the white (aka dark) icons for the appbar.
WindowsRT
This section is still a work in progress. The idea being to provide larger vector assets outside of the normal circle that the application bar is limited by.
Expression Design
All of these icons were created in Expression Design.
Tutorials
Contact
Please send icon requests to Austin Andrews (@templarian) on Twitter or create a new issue.