I keep getting a variety of sources, some saying that a plane definitly hit it, and then the ones who say missile etc.. I mean what's going on? I'm fairly convinced after watching loose change that it was a missile.
Beware of Loose Change, there's a lot of disinfo in there.
That said, I'm not sure what hit the pentagon. Using the plane (possibly along with explosives like they did at the WTC) would be logical, after all they'd have to disappear the plane somehow if they used anything else, and why not dispose of it the way they need, and generate eyewitnesses at the same time?
On the other hand, the damage to the building does look more like missile damage, I'd think a plane hitting would at least have left scratches where the wings hit.
The problem with the "no plane" theory is that IF it was planted, it can be easily refuted when the govt sees fit (there are hundreds of surveillance cameras in the area that must have some coverage of the impact!), and that could discredit the entire 9/11 truth movement. It's possible that they're just waiting for the "no plane" theory to be widely accepted (e.g. after Fahrenheit 9/11, part 2 will focus on the pentagon damage) to release hundreds of videos clearly showing the plane.
On the other hand, if nobody buys the "no plane" theory and the pentagon was indeed hit by a missile and not by a plane, nothing relevant is lost -- without the stand-down, neither a plane nor a missile could have come even close to hitting the pentagon, and of course the explosives in the WTC are all the proof we need without even looking at the pentagon.