How to remove scratches from 5th generation iPod?
I found on this site Repair iPod Scratches yourself Cheaply that you can use something called Brasso to clean the back of it. It has a mild abrasive in oil. it will cost you about 5 dollars. Then to clean the face, either a microfiber cloth or a t-shirt.

EDIT:
You could try Ice Creme its designed for iPods and Macs (or so it says).