So, lately I've been using the developer preview 0.2 version of
Songbird as my primary music library and media player. I've been looking for an open source and/or lighter weight application to replace MusicMatch for some time, so I was happy when a friend sent me a link to Songbird. It's looking nice for a 0.2 version. All the basic functionality is there, and it has a much smaller footprint than MusicMatch. It's got some missing features (the track info editor doesn't actually update the files yet, just the Songbird database, for example), and some oddities (sorting is case sensitive, so the tracks where the meta info happens to be lower case appear at the very end of the list in library view, for example) but it's definitely worth a download, IMO.