[Update 2007-09-01]
These are available here: http://www.python.org/dev/peps/pep-0020/ as a Python PEP.
19 principles behind Python from Tim Peters: http://www.python.org/dev/culture.html
Of the 19, these 9 are my favorites:
Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. There should be one -- and preferably only one -- obvious way to do it. Now is better than never. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea.
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
There should be one -- and preferably only one -- obvious way to do it.
Now is better than never.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.