[BrianG]

Any particular reason for ipod specifically? There are tons of music players on the market that you can get new and aren't expensive.

Assuming mp3 format, 2MB/min quality (generous estimate), 5 hours requires less than 1GB of storage. Pretty much all devices have at least 2GB these days. If your ride is bumpy, I'd suggest something with flash-based memory rather than harddrive. Takes less battery power too.