http://pythonbooks.revolunet.com/ - about 50 books - Another good list of free python books that is kept up to date, and I believe are all free or open-source: (I won't repeat all the books on the list here, just go check it out! Some are also on the list above, but not all)
http://projecteuler.net/ - is another interesting site to check out if you want some math/cs practice. They have 400+ math problems that you can work your way through. It's not language specific - use whatever program you want. Practice is good though!
ChekiO The Game for Coders. "Resembles Project Euler, but is Python-oriented."