I say another, because we all know the DIY MP3 Player and the AVR Butterfly MP3 Player. This mp3 player can support up to 4 GB of storage (MMC or SD cards) runs from a single AAA battery and has full user control (volume, track, pause, skip, directory) with a 5-way micro joystick.
Also the LCD has contrast control, you can record voice and the firm-wire is totally upgradeable trough RS232. In fact this DIY MP3 player is the coolest I’ve seen so far and it’s full of tricks.
EchoMp3 Another DIY MP3 Player: [Link]