Whispercast is a script that lets you stream your own MP3 library over the network. There is no additional software to install on the server (only a webserver is needed) or on the client (your existing media player will do just fine.)
The idea is simple; it makes a playlist on-the-fly for a directory of your choice. This playlist is then shipped off to your browser, which invokes your media player to play them all. Music is streamed, so you don't need to wait for an entire song to download before it starts to play.
The best part (at least for me) is that it needs no extra software, and is extremely simple to install and use. Just drop the files in a web-accessible directory and put the path to your music library in its configuration file. For more power, you can edit the configuration to customize how each line of output is displayed.
The script is licensed under the GPL, so your customizations and new features are not only expected, but also encouraged.
NOTE: This script is no longer actively maintained, but simply made available for convenience.