Mac OS X menu bar music player
I've found this app called Vox. I was looking for something similar to yourself and it seems to be the best option that I can find.
Here is an image of some of the UI (from their website, linked above):

(source: coppertino.com)
When the app is running, you also get menu bar icons like these: 
The lefthand button shows a dropdown with the 6 next songs and has a shortcut to open the full app again:

A couple of points to note:

I've found that if you have playlists organised into playlist folders in iTunes, that unfortunately it won't recognise them all.
You have to reload your music from iTunes every time you open the app.

I know this is a late answer, but hope it helps! :)