In the past two months I have been using amaroK as my main music player.
Why have I chosen amaroK? It has a beavy of features. Many of which are not available on any platform or not in any other single player.
Check out some of its coolest features.
Update: I just found the coolest feature in amaroK. You can have it append suggestions from AudioScrobbler to your playlist so you get an ever expanding playlist of music from your library.
It is using the Web 2.0 to the best of its advantage.