I use iTunes for music and VLC for movies. Both players are easy to customise too in terms of aesthetics. I tried many different players for both music and movies from open source to paid ones and ended up returning to my original iTunes/VLC combo. The selection library of music or movie players for the Mac environment is extremely limited but thanks to that I don't have to spend lots of time deciding on my ideal player.
With the recent release of iTunes 11, it just got harder for me to ditch this music player for a competitor.