What's new in Python 3.0?
or all "What's new" documents since 2.0

Tutorial
start here

Using Python
how to use Python on different platforms

Language Reference
describes syntax and language elements

Library Reference
keep this under your pillow

Python HOWTOs
in-depth documents on specific topics

Extending and Embedding
tutorial for C/C++ programmers

Python/C API
reference for C/C++ programmers

Installing Python Modules
information for installers & sys-admins

Distributing Python Modules
sharing modules with others

Documenting Python
guide for documentation authors