mt-daapd, also known as "Firefly Media Server" is super-excellent. It's a daemon that lets me share my music over the itunes sharing protocol. Having it as a daemon is a good move, I think, because it can be serving regardless of whether I happen to be running rhythmbox at that time.
Also, it lets me have a machine that lets me serve my music and does little else. There's no reason to marry the serving of music with a GUI.