Both you and Tom:
If you guys do a simple search on Google you will come up with a few things: photographs of bystanders capturing large pieces of the passenger jet in the foreground. Not just small pieces of scrap metal, but actual chunks:
http://www.geoffmetcalf.com/pentagon/images/13.jpg
Heres a civilian photo of a nearby lightpole that was clipped by the incoming plane:
http://www.geoffmetcalf.com/pentagon/images/1.jpg
Also, you have probably heard how during the attack the Pentagon was undergoing renovations, right? Wells, those renovations included reinforcing the outer structure to withstand a bomb, missile, etc.
One of the main gripes by conspiracy theorists is that after the attack, the entire Pentagon wasnt destroyed like the WTC towers. What they fail to realize is that the Pentagon is/was the most heavily defended military installation next to Norad. If you look at any other photos BESIDES the ones posted by conspiracy theorists, you can clearly see how the wings of the flight caused considerable damage to the bottom floors. Again, the Pentagon was specifically designed to prevent such a devastating attack, hence the whole thing not imploding.