I haven't used Komodo yet (the download never quite finished on the slow connection I was on at the time), but I use Eclipse with PyDev regularly and enjoy the "IDE" features described by the other respondents. However, I'm also regularly frustrated by how much of a resource hog it is.
I downloaded Notepad++ recently (much smaller download size ;-) ) and have been enjoying it quite a bit. The editor itself is nice and fast and it looks to be extensible. I'm hoping to copy some of my favorite features from IDE into Notepad++ and migrate, at some distant point in the future.
