I like Rhythmbox, The Official Music Player for GNOME, because:

• iTunes like interface: very easy to navigate and find what exactly you want
• GStreamer. Those guys rock, at least in audio.
• You can very easily drag files to any Nautilus folder, a feature I was missing a lot in XMMS (a Winamp like player - a very good example on how an inconsistent and hard-to-use application might look like)
• All in all, it's simple.

What I would love to have with it is, a good equalizer but it's more of a GStreamer thing than a Rhythmbox one.

Enjoy,