There are a couple of popular sites that list or host submitted Python modules.
[http://pypi.python.org/pypi The Python Package Index (aka "PyPI")] is the current preferred location to list packages. It is integrated with the distutils in recent versions of Python: you can upload distribution files to PyPI so that the code will be available for downloading. See the CheeseShopTutorial or [http://docs.python.org/dist/package-upload.html Uploading Packages to the Package Index] for more information.
[http://code.activestate.com/recipes/langs/python/ The Python Cookbook], for small useful snippets of code.
There are a few other less useful or older sites, in case you are searching for code and the above didn't help.
[http://www.uselesspython.com/ Useless Python] is indiscriminate, for all bits of code you don't think are worth publishing.
[http://py.vaults.ca/apyllo.py Vaults of Parnassus] - a link store for Python modules. You must host files elsewhere, but this is one of the oldest and largest lists of available Python code.
[http://www.pycode.com/ PyCode] - an older site where you could share modules. No activity since 2006.
- This wiki - if a module is relatively short
See also: Italian translation at ["Codice"], [http://www.faqts.com/knowledge_base/index.phtml/fid/235 FAQTs] section on module Q&A, ["Code"]