Here's a photoshop file I've created for making custom folder icons for your desktop icons. I use it on my personal and client projects to help keep things organized and easy to see at a glance.
Also, I use this great app, Icon Slate, for creating the actual icon files after I've exported a PNG from photoshop. I highly recommend it if you want to create actual icon files from this photoshop file.
Hope some people can get some use out of it. Enjoy!