I'm a little into the second hour of the five hour documentary from National Geographic called
Inside 9/11: Commemorative Edition. It's a two DVD set.
This thing is great. It never gets slow and provides (so far) the background of how 9/11 came to be. From Osama gaining his fame by being a soldier in the Soviet-Afghanistan war (did you know Al Qaeda basically whipped the Soviets with American provided ground-to-air missles?), to Saudi Arabia turning down Al-Qaeda's request to fight back Iraq after Iraq had invaded Kuwait (they turned to the U.S. instead which angered Osama to no end), to President Clinton turning down a chance to capture Osama (because Osama, at the time, was on a hunting trip with the prince of the United Arab Emirates.) Great stuff.