Spinsanity, which I haven't mentioned lately, is probably the best site to find an unbiased, fact-based analysis of some of the more egregious distortions and fibs in politics these days. Once in a while, I think they get a little absorbed in parsing precise words as opposed to the effect a speaker manages to convey, but the guys there are generally very good debunkers.
They just posted this article which discusses Fahrenheit 9/11. In a couple cases (the stuff about John Ashcroft being defeated by a dead guy, for instance), I think they're examining a joke as if were presented as a literal statement of fact. But apart from that kind of thing, they're on target.