What are the usable tools?
I am aware of wxformbuilder and wxGlade, but none of them seems to be complete yet.
Here are a few of the most popular wxPython related GUI builders:

Boa Constructor (mostly dead) 
wxGlade
wxFormBuilder 
XRCed 
wxDesigner (not FOSS)
Dabo - one of their videos shows a way to interactively design an app...

I personally just use a Python IDE to hand code my applications. My current favorite IDE is Wing.
What are the existing open-source Python WxWidgets designers?