LightMP3 is a simple mp3 player whose goal is to preserve battery life.

Features:

-Browse all your ms
-Play a single file or a whole directory
-Can play mp3 up to 22mb (no streaming, sorry)
-Displays information on file (including ID3v1)
-Works with psp remote.
-Can play a 128kbit mp3 at 70mhz CPU and 54mhz BUS

http://forums.qj.net/f-psp-development-forum-11/t-releaselightmp3-111753.html