Are you developing for Windows 7 Phone? Recently at MIX10 in Las Vegas Microsoft made their Windows 7 Phone Series Developer Tools Available so developers could start to create applications for the new phone that are due to come out later this year.
Well they have posted a zip file for download that contains 64 application bar icons for you to use in those apps.
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.
You can see an entire list of icons that are available in this download at the Application Bar Icons for Windows Phone 7 Series download page.