A perfectly valid reason for not using iTunes is that it wants to add things to the library instead of just playing files it is given. When you want to work with 200gb+ of tracks already sorted by directory on external drives this just doesn't work.
I have found library based mp3 players abhorrent since their conception and generally avoided them. It's a shame winamp isn't available for OSX, name aside it is my favourite option for windows. I don't like foobar for the same reasons I got a mac instead of using Ubuntu.
Anyway, opinions aside, check out Vox. It's a small simple work-in-progress Mac player (for many formats).
http://www.voxapp.net/