So what about other MP3 players? well, it'd have to have either massive ammounts of storage or really cheap storage extensions (and even they would have to be rather large). I've been doing the mp3 thing for a bit now and have a not-inconsiderable collection. Add the fact that I refuse to record in anything other than highest-quality vbr and you can see the storage needed skyrockets rather quickly. A small sampling (suitable for this purpose) would itself take a few GB.
Given the above, an iPod just seems the best choice. Much though I hate the fact that it has moving parts, I know of no other solid-state mp3 player that meets my needs. Besides, the iPod has some fringe benifits such as the wired remote and such that almost make up for the fact that it's HDD based.