The Windows Phone Developer Blog have kindly released the Windows Phone 7 Series Icon Pack to download.
We’ve just release 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.