This category is interesting this year since all of the films are highly topical and controversial -- no penguins in this category (but you can find them among the "Best Animated" nominees). The first documentary is Al Gore's Inconvenient Truth, about global warming. The next is Deliver Us From Evil which follows a catholic priest who is a molestor and his victims. Then there is Jesus Camp about how the religious right creates a new generation. Then there are two films documenting the conditions in Iraq for Iraqis (Iraq In Fragments and My Country, My Country).
The conventional wisdom is that two of the same film usually cancel themselves out -- so that would rule out the Iraq movies. I think Jesus Camp will make too many voter feel uncomfortable. Deliver Us From Evil is very much like Capturing the Friedmans to win, as Capturing the Friedmans lost out to The Fog of War. My vote goes to Inconvenient Truth.
Go Al Gore!