IDEs, Extensions, and Tools 

IDEs
 IDLE (included in standard distribution)  free http://www.python.org
 Pythonwin (included in win32all install)  free  
 Boa Constructor - wxPython GUI Builder  free http://boa-constructor.sourceforge.net/
 Komodo v1.2  $295 http://activestate.com/Products/Komodo/
 ActivePython v2.0 - MS Visual Studio plugin  $295 http://activestate.com/Products/Visual_Python/
 PythonWorks Pro v1.3  $395 http://www.pythonware.com/products/works/index.htm

 
Useful extensions and tools

Numeric -- fast numerical computation (arrays, matrix manipulation, FFT, and more) http://www.pfdubois.com/numpy/
documentation (PDF)
Psyco -- specializing compiler akin to a JIT http://homepages.ulb.ac.be/~arigo/psyco/
Pyrex -- Python to native libraries http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/
PyInline -- imbedded C code in Python scripts http://pyinline.sourceforge.net/
pSQL -- makes SQL access look like dictionary access http://fionn.dhs.org/software/psql/
Anygui -- a wrapper API for a large number of underlying graphic toolkits http://www-106.ibm.com/developerworks/library/l-anygui/
SWIG -- "automatically" wraps C/C++ code to make Python extensions http://www.swig.org/
Tkinter -- GUI toolkit included in the standard Python distribution and installation
http://www.pythonware.com/library/tkinter/introduction/
Pmw -- Python MegaWidgets, general extensions to the Tkinter GUI toolkit http://pmw.sourceforge.net/
BLT -- MegaWidgets for graphs http://www.ifi.uio.no/~hpl/Pmw.Blt/doc/
http://www.pythonware.com/library/tkinter/introduction/
Plotting -- various libraries http://starship.python.net/crew/jhauser/plot-res.html
PIL -- image processing http://www.pythonware.com/products/pil/
mcrypt -- cryptographic routines http://mcrypt.hellug.gr/
HTMLgen http://starship.python.net/.../HTMLgen/html/main.html
http://www.python.org/topics/web/HTML.html
Zope -- a free, Open Source web application server http://www.zope.org/