DioPlayer is a completely free MP3 and WAV player.
Most of the functions are exactly what you'd expect from a music player: play, pause, stop, forward, back and so on. DioPlayer also has an 8 channel graphic equalizer, support for playlists and a display compatible with ID3v1.
As well as these functions, the player works well in the background, has skins that fit two resolutions (160x160 and 320x320) and it's compatible with expansion cards (sd/mmc).
A full-featured, free music player for your Palm.