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.
If you're referring to writing .ui files, the Qt Designer that comes with PyQt is sufficient for layout of widgets, and pyuic4 will convert them to Python code for you (pyuic4 comes with PyQt).
Eclipse
PyDev
