While it's still in beta, Songbird is fairly mature so far as I can tell and it totally ROCKS!! It's like somebody took Firefox, iTunes and WMP, mashed them all together and sprinkled on a bit of attitude. It's fully skin-able and has quite a few really good plug-ins already, not to mention that it's easily integrated into Last.fm. I've been pushing it around a bit and haven't had any real issues so far, I just continue to be more and more impressed with it. Now, I know you guys think I'm this crazy, nut-job open-source advocate but this one is really worth checking out.