Windows 7's new Libraries are one of the best underhyped features because they make it easy to manage files across multiple folders—the only problem is that all of your libraries use the same bland icon.
Change all Icons in Windows 7 and Vista Using Default Programs Editor in Techno PIRATE
All the utility actually does is provide an easy interface to edit the XML file that represents each library—so if you are more of a hands-on type or want to understand how it works, I've also written up a quick guide on how to edit the library icons manually using Notepad (or your favorite text editor). Replace Librarie Icons is a free download for Windows only.
source Techno PIRATE