I think this might be my new MP3 player. This MP3 player uses cheap MMC for storage, powered by a single AAA battery running a 20 Mhz chip which can play files up to 256 kBps at 44.1 kHz. ID3 support, Nokia LCD screen, micro joystick, not bad at all. Full schematic & pcb, hex file available. I think encasing this in clear lucite would be rad. Link.
DIY MultiMediaCard MP3 player