One of my colleagues Jeremy Foster created a blog post with some GREAT resources like Metro Tiles, Visual Studio Add-In, and Art Tools. Check it out if you are trying to ramp up on Windows 8 Development.
http://www.codefoster.com/post/2012/05/17/App-Accelerator-Resources.aspx
-Scott
(Originally Posted on scottkerfoot.com Blogengine.net blog and manually migrated to WordPress on 10/20/2017 for Historical reasons)