What is your favorite documentary?

I realize that documentaries often present a narrow-minded view into a particular subject, but they can often times be just as entertaining as feature films.

My favorite documentary would have to be Lake of Fire (2006) by Tony Kaye. It presents, in my view, a fairly non-biased look on the pro-life vs. pro-choice debate, with some compelling arguments for both sides.

This sub-forum is rather barren, but if you stumble upon it by any chance, let me know what your favorite documentary is.