PyQt is a set of Python bindings for Digia's Qt application framework and runs on all platforms supported by Qt including Windows, MacOS/X and Linux.
WxPython is a Python wrapper for the cross-platform C++ GUI API wxWidgets.
"Two words of warning against wxpython it is not possible to install it via the popular fink package manager on mac os x currently which makes it far less portable than pyqt and tkinter"
from question "Python GUI for portable app"
"Wxpython is probably easier than pyqt or tkinter i don t want to start a framework war"
from question "How to create a GUI table in which the users can input data in Python?"