I'm using the pydev extension to
Eclipse for Python development.
Snappy, works in Windows and Linux,
pretty nice debugger (comparable to
the Eclipse Java IDE debugger). The
code completion is able to tie into
the PyQt modules as well.
PyQT can be a hassle to setup in Eclipse but when it is set up it works pretty nicely! There is a guide at popdevelop that shows you how to setup Eclipse in Windows to work with PyQT, with code completion and all.
