WebMplayer is a free webbased frontend for Mplayer to manage and play music-files & audiostreams (translations available in English, Dutch and German).
mp3 player for Notorious Image Productions.
PHP::Playlist is web interface to your music. Supports streaming, mp3/ogg tags indexing and searching, download statistics, RSS feeds and more. Writen using PHP/Perl/SQLite3.
Spiffy List will generate .XSPF playlists for the popular Flash based "XSPF Web Music Player". It will allow users with no knowledge of XML to use a GUI to edit their playlists.