I found I needed more complete RFC 3548 support for a project I'm working on. This RFC contains the most up-to-date specification of Base64, Base32, and Base16, including a description of alternative alphabets, etc.
I didn't want to create any new modules, so I modified the base64.py module to include a bunch of new functions, leaving the old API unchanged (i.e. encode(), decode(), encodestring(), decodestring()).
I have new functions with docstrings, and an updated unit test. If you folks like the API I've chosen and are generally in favor of my changes, I'll update the documentation as well.
The patch is available here:
Currently assigned to Tim for review.