If you're paranoid about marring your iPod nano's gleaming finish (and I don't blame you, given how easily these babies scratch up), check out YoTank's iTank cases.
These bulky bruisers, also available for other iPod models, encase the Apple players in thick metal.
The nano-style iTank I borrowed is a two-piece affair with six screws that are removed with a special tool. This is serious protection, but it makes a slim nano grow to about the size of an iPod mini (not a problem for routine use, but probably not what you want for jogging or the gym).
See the YoTank site for other metal-case options, including a version for Creative's Zen Vision:M.
