Python is a great interpreted language for either scripting or proper applications, and I've mentioned it a few times in the past, it really is that good.
I came across a great site about GUI kits for Python. It gives you suggestions based on your requirements by filling out a mini form.
PyGUI - It is planned to be a cross platform GUI library implemented specially for Python. Currently it has Mac OSX Cocoa and X11 using GTK implementations.
Tkinter - the default GUI installed with Python. It provides a thin layer to Tcl/Tk.
wxPython - I have mentioned this a few times already. It is the Python bindings for wxWidgets making it cross-platform and with a great depth of features. You can also use a Python written IDE and RAD GUI designer BoaConstructor.
There are many more listed on the page covering the GUI designers as well as the toolkits.
