Asa points to Songbird, a new media player built on Mozilla technology. The application interface is built with XUL, similar to Firefox and Thunderbird. It’s from the same people who built Winamp 5 and Y! Music Engine. It looks great. It has iPod support and the developers say the program will eventually contain everything you’d expect from a media player.
See the screenshots at the Songbird blog. Kinda feels like Itunes. I’m not sure if Songbird is going to be open source; I suspect possibly not as there is no mention of it on the website.