Work on MusicMan has been discontinued, as a friend of mine has a far more capable player in the form of Morrigan, and it is probably easier to port the features I would like to see than continue writing my own client from scratch.
MusicMan is a cross-platform music player and library organiser. It supports multiple music directories, each of which is recursively scanned to build your media library. Your library is synchronised with the actual files on disk each time you start MusicMan. It also supports mass ID3 retagging and dynamic searching (iTunes-style), where entering a search term reduces your current playlist to only the songs that match your search.
MusicMan is early alpha software. Lots of things (e.g. playlists, Shoutcast) don't work yet. However, please try it and submit any bugs you find or features you would like to see on the issue tracker for this repository. I've not yet put the source code anywhere that people can easily commit to, but if you feel like adding/fixing things in the meantime, send the source back to me and I'll merge it in.
You can download MusicMan here (Extract ZIP, run MusicMan.jar)