I saw a pointer on MAKE Magazine to a $9 MP3 player. It's fairly simple, and reads SD or MMC cards. I am pointing you to the article, because there are lots of ways this could be used interestingly as a hack. For instance, you could keep a few around the house in special areas to help people remember things. They might be useful to people with disabilities. You could use it to keep notes for class.
It just seems useful to have a nine dollar player, were something to come up that you wouldn't want to use a $100 player.
Nine Dollar MP3 Player — [MAKE]