Here is a "sample application" to demo Sjeep's sjpcm 2.0 : a port of libmad and a mp3 player, with source ;)

It is compiled for PAL but can be changed for NTSC (see readme.txt). To test it, place a 48 KHz encoded id3tag-free mp3 file named test.mp3 in mp3play.elf dir and naplink the .elf to your favourite console (if you painted it orange, I don't assume any liability in case of big trouble).

look in cvs for libmp3, a library that uses this very code.