Unfortunately, there is no easy way to adjust the balance on an iPod as Apple designed the iPod without a balance adjustment feature. However, there are alternative measures that can be taken to adjust the balance on an iPod by using third-party hardware. Finally, Apple has a specific feature request where users can request that Apple add a certain feature to any of its devices. If you are interested in a software balance adjustment feature, request it. (See Resources)
Use balance-control headphones. Plug them into your iPod. You can control stereo balance directly on the headphones.
Purchase an in-line volume-control device. (See References)
Connect the in-line volume-control device to your iPod.
Connect your headphones to the in-line volume control.
Turn on your iPod, you can now control stereo balance by adjusting the channels on the in-line volume control.
It is possible to adjust the stereo balance of MP3 files before uploading them to your iPod. If you have a hearing impairment and wish to adjust the balance of all of your MP3 files permanently, this solution will be more cost effective but will require a lot of time and patience.
Remember that as with any in-ear listening device, if you adjust the volume to unsafe levels you can permanently damage your hearing.