The wxPython Demo
Some nice guis can be found in the wxpython demo. Actually the demo is a GUI ;-)
GUI2Exe
Another interesting example is GUI2exe from Andrea Gavana an expert on wxpython and a prolific widget creator.
SPE
And finally, my recommendation is Stanis python editor (SPE). Here you will find all kind of stuff (interpreter shell embedded, third party applications neatly integrated in the main program, code editor, and more...) everything running on wxpython. SPE is just about good design both in terms of code and of usability. It runs in windows and linux. Stani is also the author of Phatch another application based on wxpython mentioned in one of the comments as a good example of design. These and other facts about this guy are not coincidences...
DABO
I forgot to mention Dabo:
Dabo is a 3-tier, cross-platform
application development framework,
written in Python atop the wxPython
GUI toolkit. And while Dabo is
designed to create database-centric
apps, that is not a requirement. Lots
of people are using Dabo for the GUI
tools to create apps that have no need
to connect to a database at all.
Dabo has a demo GUI build-in that allows to create/access your database and manage the data.
Editra
Ooops I forgot also editra a multilanguaje editor/IDE (still I prefer SPE although SPE is python specific). One interesting feature is that Editra can be extended with plugins.
I use all this programs myself in windowsXP.
Later Edit: two more applications using wxpython:
PyChem
Another application I use for my research tasks is PyChem. PyChem is an application for data analysis (classification, PCAs, etc). Like Gui2Exe, but differently to others GUIs mentioned above, it uses 'new style' widgets ('2D feeling'), so it is interesting in this respect. It shows how to implement data grids and several kind of graphics, and makes intensive use of numpy/scipy and biopython libraries.
BoaConstructor
Not sure if it has been mentioned before. BoaConstructor is one of the classic python IDEs. I have not used it very often myself because I feel more comfortable with SPE combined with wxglade (hell! wxglade is another wxpython application!). It combines GUI building with code building. Unfortunately I'm not sure about how alive the project is. Maybe you should check SVN because the last builds were made in 2007.