If you are looking for an interactive environment and not needing to code modules, I would suggest IPython. Though this is developed with scientists/statisticians in mind, it will run just as well without any of the scientific packages installed. The features are powerful, with code completion, integrated help, integrated debugging, etc., and it functions as a notebook with Markdown and MathJax integration. By far the best choice for those that need powerful features without wishing to load megabytes of GUI into RAM--since it is browser based, it is used in your always loaded chrome/safari instance. ;-)
