If you are using a Mac, and like GUIs, then TextMate is my suggestion. It's not a full fledged IDE like Eclipse, but it does have a number of nice features above an beyond a simple editor.

Personally I have found that IDEs are much more useful for more compiled languages like Java, etc. where they take away the headache of manually twiddling with build scripts and tools. The "scripting" languages (Perl, Ruby, Python, etc) all have decent enough command line UIs that wrapping it in an IDE seems overkill (again, this IMO).