Just joining the fray even though this thread is a bit stale. I have the very good Sansa M260 (I think that’s the number) the 2gb model. It runs on a AAA. Yes, it would be cool if it could run on a AA instead and if it could take a microsd card.
To say there’s no market for these things is a bit harsh. There’s a huge segment of users out there who are not that comfy with computers to charge things, or simply want to load on music like we did in the days of walkmans and cassettes. I’m thinking of my parents, but it could just as easily be a techie type who doesn’t want to be tethered to the computer all the time - like me.
As I say, the m series was a great first step - thanks to Sansa, and consider that the market is waiting for you - if you advertise on tv and radio and attract a segment not currently able or happy with mp3 players.