I know there are a few OS X fans on here, though I'm not sure how many use emacs.
If you do, Aquamacs seems to be a great emacs package. In particular, it supports Mac keyboard shortcuts as well as the standard emacs shortcuts. This is very nice if you're (e.g.) copying and pasting between a regular Mac application and emacs. I don't know about you, but I can get my mind in either '"emacs mode" (ctrl-y to paste) or "Mac mode" (command-v to paste), but switching back and forth between the two is highly annoying. It also uses the standard Mac method of opening a separate window for each buffer, rather than the emacs way of having only the active buffer visible (unless you split the window).
I've been using this for about a week, and have been quite impressed.