This is a very good blog-posting and i fully agree with it:
Idle is really only useful to teach the first steps of python. As soon as leaving the interactive mode, i force students to use a different editor than idle, mostly geany.
On the other hands, Geany does most things right out of the box: Line numbers, pretty code navigation panel, color chooser to get rgb codes, font size changing with mouse wheel, to name just a few.
Until i find a better solution i will stay with Geany. I wish it would be shipped together with python and run out-of-the box on every major OS.