Here is an interesting case for the iPod Touch, the Surge case from Novathink, which will recharge your iPod via the built in solar panel.
The Surge iPod case features a 1500 mAh 3.7 V lithium-ion battery, that will give you up to 120% extra power for your iPod, and it can be recharged via USB or via the built in solar panel on the back.
