Create your own desktop themes by modifying every single icon, from the My Computer one to the one for the Recycle Bin, as well as shortcuts, the Start Menu, disc units, folders, and more. You can also create a new theme by modifying your current one, so you can identify more easily which icons you want to change.
Bee Icons is great for managing and replacing icons on your system.
Works for 30 days. You need AwIcons to edit icons. You can download it here.