To begin with you may use the default python IDLE or Eclipse with pydev plugin. Also you may check "SPE IDE".

If you're running KDE (e.g. Kubuntu), Kdevelop is kind of decent, too.

Use vim. See the article at http://blog.dispatched.ch/2009/05/24/vim-as-python-ide/

I prefer emacs for all my development and python is no exception. With a little bit of tweaking one can turn emacs into a powerful python IDE complete with syntax highlighting, auto completion, and more. Couple that with a split screen running a python shell and I cant imagine being any more productive. That is, unless you are an avid vim user ;)

Here are a few good tutorials to get you set up and running.

http://hide1713.wordpress.com/2009/01/30/setup-perfect-python-environment-in-emacs/
#you'll need to read the comments for some necessary corrections on this guide, specifically changing some of his backticks to commas in the lisp code.

http://www.enigmacurry.com/2008/05/09/emacs-as-a-powerful-python-ide/

hope this helps.