It's an open-source program that aims to be the Firefox of Media Players. It's open source - is based on Firefox - and is already supported with extensions and themes (cleverly called Feathers). It'll sync with your iPod, connect with LastFM, and automatically pull up the Wikipedia entries on your Artists as their music plays (plus quite a bit more).
I just downloaded it like an hour ago and I'm giddy over it. I've been looking for an iTunes replacement for a while now and this is pretty sweet. I'd give it a look - I know it's only a developer's release at the moment, but it's definitely stable.
http://www.songbirdnest.com/