ScrIDE is a free OS X based IDE for the Python programming language by Glenn Andreas. It includes a syntax coloring editor (with function popups navigation, quick open of included files, splitable panes, tooltips, completion) source level debugger, online embedded help, interactive shell windows (including "inside" debugging), and a whole lot of extensibility. It does not require any specific version of Python or third party add-ons (since it runs python processes "externally" it can be configured to even work with multiple versions at once).
Homepage: http://projects.gandreas.com/scride