Windows 7 Amazing Library feature is one solution if you deal with lot of folders every day and eekp on changing folders to get in there. Though its cool and lets you create new Library also but there si no way ( Yet ) to change the icons which is a great way to differentiate libraries from one another. By default you get a general icon.
Replace Library Icons is small application which lets you change any of the Libraries icon and in case you dont like it, you can revert back. You can choose the icon from DLL or ICO file.