You'll probably get a lot of opinions with iPod cases. Sometimes they are good, sometimes people report that they actually scratch an iPod.
Some iPod cases can be found at Apple's online store:
http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore.woa/wa/RSLID?find=ip od+case
Be sure to click "Next" to go to the further pages to see all (or more of) the results for iPods cases.
Also, you might want to search the Discussions for suggestions with specific iPods cases; this is a question that is asked very frequently, so you might find more answers by searching the Discussions:
Apple - Support - Discussions - Search Results: ipod case
Sorry I can't directly suggest any specific ones, but searching for various answers on here might really be helpful.
-Kylene
