Dock Media by EKlecticCore is designed to be a minimalistic yet full-featured media player with an emphasis on displaying embedded art and "side-car" fan-art image files.
Example of Dock Media in minimalistic view with controls:
Example of Dock Media smallest/least-obtrusive view:
Example screen shot (not an endorsement):
Example screen shot of rotating fan-art / folder images (not an endorsement):
Dock Media currently playing with media images disabled (song list view):