Do you want to hear free music? Free as in freedom? Here you may find some links to free music, which you may play on your Linux PDA, Linux laptop or portable MP3 player. Many of them are published under a free license, e.g. Creative Commons, GPL. Not much yet but I hope it works as a start. If you know of something missing here please let me know.
You may look up a survey of Linux apps for portable music players.