I'm not sure if this is so much of an issue in the USA, but in Europe, iPods have their volume limited due to EU regulations to stop us deafening ourselves. This can be removed by means of a simple software update (which isn't endorsed or promoted by Apple in any way). I found it gave me an extra 50% on my volume.. I can hear things now!
You can find out more about it at
http://gopod.free-go.net/index_en.htm