The state of Lisp programming on OS X is quite good. Things I've tried:
* Clozure MCL, excellent Mac integration no need to use Emacs
* LispWorks, good Lisp IDE, free for personal use, no
need to use Emacs
* PLT Racket, good Scheme IDE, no need to use Emacs
* Clojure, Cake make's it a cinch, you can use TextMate
If you're going to go with Emacs, for Common Lisp, Cocoa Emacs 23 plus Slime is great, Cocoa Emacs 23 plus Quack for Scheme is great.