Microsoft released a package of application bar icons for developers building apps/games for Windows Phone 7 Series. This package contains a set of 64 app bar icons that you can use when developing applications for Windows Phone. In addition to the 64 icons in PNG format (32 dark and 32 light), this package also contains vector versions that can be easily imported into Microsoft Expression Blend 4 Beta when using the Microsoft Expression Blend Add-in Preview for Windows Phone. For more information on how to use these icons within your application, see How to: Add an Application Bar to Your Application on MSDN.
Download: icon pack