Capturing Reality: The Art of Documentary is a documentary film about documentary films.
Errol Morris, Werner Herzog and over 30 of today's top documentary filmmakers provide an in-depth look at non-fiction filmmaking and the steps to making a documentary. These masters of the craft reflect upon the nature of documentary as a form of storytelling and offer insight into their approach to the 'truth.'
The trailer is here and there are lots of clips up on the site; here are two featuring Errol Morris and Werner Herzog. (Man, I could listen to Herzog talk all day long.)