My choice of cases is going to be a little biased because of the fantastic results I have had with my 4th gen ipod. The case I use for ipod nano is the iskin duo.
Pros:
- Amazing protection from 2 covers (ala the word duo) that covers the screen and the ipod click wheel.
- Material used for the cover is the same that is used with all of their other covers. (my 4th gen eVo2 has never given me problems and is durable).
- Glows in the dark =P (yeah not really a pro, but still cool none the less).
- Makes the nano better to grip with the cover. (the ipod nano has always been too small for my hands, but thankfully with the 1cm worth of covering, and the sure grip edges on the sides).
Cons:
- Kind of crappy color selections compared to eVo2 line up (I choose the carbon / orange one and love it).
- Pricey, pricey and more pricey $$$ (30 dollars for a case + shipping can all add up in the end)
- it seems like my headphone port is going fall out anytime soon when I have them connected.
The ipod lounge highly reccemends it and has given it a great review for the product.
http://www.ilounge.com/index.php/reviews/comments/iskin-duo-for-ipod-nano-ipod/
if you are interested in purchasing one, heres their site:
http://www.iskin.com/duo_nano/features.html#
If you don't mind the color selections, get this case for your nano. I will trust no other company then iskin when it comes to protecting my new ipods.