CATEGORY IMAGES
You can add images to the categories list. In this directory you will find some icons examples used in the admin back-end, if you find the useful you are able to use them.

On the internet there are many webs where you can find and download icons, this is a short list that might help you.

http://www.clipart.com/
http://www.iconbazaar.com/
http://www.mediabuilder.com/
http://www.freegraphicland.com/
http://www.designandcreate.com/graphics/