I made a small collection that I think are the best and most well known, it is clear that this is based on my tastes so I strongly recommend to comment on this post which is more suited to your tastes:
Amarok: which i like use every day to listen to the music, a lightweight player that has everything you need, multiple playlists, integration with other KDE applications, it downloads lyrics from the Internet, socialized through Last.FM, information of the artists on wikipedia, apparently set by CSS … as you can see an endless list that makes it my favorite player without doubt.
Exaile: uses GTK + and the features I’m very similar to those found in Amarok.
Banshee: I have to stress this for its ease of operation. And the library is great for people who have a large collection of songs on your hard disk. You can access them and find what you want to hear quickly and conveniently.
Other alternatives which have quite good that I recomment are, Listen, BMPx …