We've seen a few of these before but this mobile iPod battery pack is definitely the simplest. It just uses two 9v and two AA's. This method could potentially (but unlikely) be harmful to your iPod since no control circuitry exists, but it's doubtful anything bad would happen.
Here's one more truly unique ipod battery charger. This project was created to harness the power of a person bicycling to charge an ipod. The project write-up has a detailed walk through of how it was created & how it works.
This article points you in many different directions for mobile Ipod battery packs. Some of the battery packs are commercial, others are homemade and use standard AA batteries. Overall, if you're an Ipod & DIY lover you won't want to miss this article as a mobile battery pack can save you from hours of boredom.
This is a very simple write-up that details how to make your own USB charger for your I-Pod. It's actually not very complicated but the procedure must be done delicately so that no wires are crossed. The write-up is in depth and has lots of pictures to guide you, so take a look.
For Apple/Mac lovers the embedded world is not very friendly. There are very few IDE's available for OSX and beyond. However, this tutorial for the AVR, guides mac users on how to get everything interfaced & programmed with minimal effort. Software examples & walkthroughs are included.