A good wxpython GUI builder?

There is wxGlade. Here is a screenshot:

and wxFormBuilder

Also, have a look here for more alternatives: GUI Programming in Python

In addition to those, some people really like the XRCed application that's included with wxPython. Basically you create your GUI in XML. There's also the defunct Boa Constructor that I see people still using on the wxPython user's list.

I've tried a few, and the only one I seem to have any luck with is wxFormBuilder

In a long ago day, I tried them all and found Anthemion DialogBlocks to be the most professional of the bunch. Along with that goes the fact that it is commercial software.

It's by Julian Smart, the creator of wxWidgets, so I suppose it's not too surprising that it's a quality product. At $90, it's a bit expensive but not outrageous.