Sane

I can't make any personal recommendations, since I've only used wxPython and TkInter. But here's a good link that might help you out:

http://wiki.python.org/moin/GuiProgramming

It includes information about every toolkit available, tutorials, links to the official sites, and all sorts of good information.

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Waterloo's Canadian Computing Competition (CCC) - Stage 2 Problems, Solutions, and Test Data