The doco is 'Religulous' as pointed out by dontaskme.
...and it's Bill Maher who made it, not the equally brilliant Jon Stewart.
Anyway enough of my anal pedantic correction...if you want to see a true pro at debating christians, check out Matt Dillahunty on 'The Atheist Experience'.
It's a talkback show that operates out of Austin, Texas and although he is not comedic or as polished as the aforementioned duo, he is possibly the most concise and devastating debater I have ever witnessed.
Most likely due to a strict christian upbringing that arms him with a thorough knowledge of the bible that is oft quoted by his hapless callers.
Very dignified though he attempts to persuade indoctrinated callers to question their belief system without outright belittling.
(on Youtube)
