Pydev for Eclipse, as others have mentioned, is good.
Netbeans has a beta Python plugin that is a little rough around the edges, but could turn into something really cool.
Additionally there is a long list of programming centric text editors for the mac, that may or may not fit your needs.
- Textmate - costs money, people love this program, but I haven't used it enough to see what all the fuss is about.
- Jedit - Java based text editor, has some nice features, but the startup time isn't great (due to Java).
- CarbonEmacs - Decent Emacs port.
- AquaEmacs - Better Emacs port.
- TextWrangler - Lite, free (as in beer) verision of BBEdit.
- BBEdit - The old guard. The defacto editor before Textmate stole its limelight. Expensive.
- Smultron - Very nice editor, the UI is similar to Textmate.
- Idle - Python's own little editor, has some nice features, but also some major problems. I've personally found it too unstable for my usage.
- Sublime Text - This is really sweet text editor that has some surprisingly good Python support.
- Pycharm - Another solid full on IDE for Python.