Before the Creative Labs Nomad, there was the Personal Jukebox, a project of Compaq Research that is sold commercially. Up to 20G hard drive, 8 hours playback on one LiON battery charge, USB connection to PC/Linux/Mac with a SourceForge'd SDK. It even (like the iPod) has Minesweeper. ;)
That said, the UI is pretty clunky (you can try it out in the Java applet emulator) relative to the iPod, and USB is really slow for transferring 20G of MP3's. The device is also significantly bigger than an iPod (though smaller than a Nomad). They have solved the "gaps between songs" problem, though.