I certainly do not believe that the Pentagon was hit by anything other than an airliner. However, one piece of evidence given by the conspiracy theorists relates to a security camera video that was trained on the spot where the plane hit. Still images from that video have been released on the web, but the video itself is supposedly confiscated. Does anybody else know why that is, or any other details around the video?
The reason you see only still image from the security camera is because it video reccorded only one frame every second... nothing was confiscated and hidden.
The slow frame rate is common in security cameras because they are mostly interested in scene changes, vehicles. and people, not 530MPH jet aircraft crashing into the building.
In addition, to fit a whole day's surveilance on a video tape at anything near enough resolution to see anything requires a slow frame rate.