NetBeans for Python is my current favorite (lighter and so much easier to install than Eclipse I found). Supports simple refactoring, autocompletion, errors/warnings...
Eclipse Aptana PyDev probably one of the most complete free IDE nowadays (haven't tested a lot)
Wingware Python IDE a commercial IDE, which has some Django-specific project setup features the ability to debug Django template files.
IntelliJ IDEA Ultimate Edition another commercial IDE which has also a plugin for Python that is under heavy development. I saw some demo which look very promising on the auto-completion (for templates and Python).
Vim which I still use a small touch-fix application. See also: Extra tweaks for Django.