There's some great icons available out there for Windows libraries customization. Use the great tool from bluefisch200 (which unfortunately doesn't seem to have a name) to apply the ones you choose. Note that I won't post all icons here- just the ones you should use.
Compilation of some nice icons and the library icon template below results in a great place to start- Windows 7 Library Icons
Nice Visual Studio Library icon for your development projects
Tons of great options at http://www.proicons.com/
Use the Win7 Library Icon Template if you want to work on your own.
