Songbird
Songbird is the Mozilla-powered open source alternative to iTunes. It's not commercialized like iTunes, so instead of closing you to a music store, you are open with Songbird to hearing music from mashTape, Last.fm and SHOUTcast radio. The playlist display is similar in Songbird as it is in iTunes, so it will be easy for you to switch over. The developers of Songbird, Pioneers of the Inevitable, are attempting what Firefox did to Internet Explorer, but with Songbird to iTunes. Songbird is an exciting experiment for the open source community.