I started my IronPython musings with Notepad++ since it's my usual text editor (after being enamored with Textpad for many years, I moved on - lots of reasons, perhaps I'll blog them later). As time passed and my scripts grew in size I started using an old version of Komodo I've got which has decent support for Python. I used Komodo (3.5) when I was writing a lot of Perl and it worked pretty well for that, especially since it had a good enough debugger and CGI emulator for me to dig myself out of holes. Komodo does okay with Python but I've been using Wings IDE on recommendation from fuzzyman and it's much more responsive and fluid as a development environment. Additionally, I got Komodo when there was still a cheapo version but now it's quite expensive - exceeding the Wife Acceptance Factor for experiments (WAFe). Wings is quite reasonable, I'll start with the Personal edition and if I can get my company onboard I'll ask that they upgrade my license.
Unfortunately I still need to run my scripts outside the IDE environs since Wings isn't built with IronPython support (correct me if I'm wrong), but I'm quite used to this now.