A great place to start is learnpython.org. It's got simple tutorials as well as an interactive shell so you can try it out as you learn.
There's also Dive Into Python, a free book that's also been published by Apress.
Dive Into Python covers Python 2, but there's a Python 3 version available as well for free, published by Apress as well.
Of course there are a lot of other free resources available, but less is more, and these two are a great place to start. A more comprehensive list of resources, free and non-free, are available here: http://wiki.python.org/moin/PythonBooks