Here's a quick summary of the arguments made at this blog about why there is no real evidence that planes hit the Twin Towers, and why there is strong reason to believe that false images were broadcast on 9/11. I will fill in the arguments with more links as time allows. Many of these ideas are not my original ideas, and I have tried to cite to original 9/11 researchers and be faithful to what they said.
1. Impossible crash physics, well illustrated by the Purdue animation.
and this recent interview of Joseph Keith, an engineer who worked on airframe testing for Boeing and says the planes would grind against the towers, not meld into them:
2. Impossible debris location, which physics professor Steven Jones has not been able to explain.
3. Witnesses who were in a position to see a plane, but did not.
and these accounts I just learned of, which are perhaps the most compelling:
Some witnesses that claim to have seen a plane appear to be lying, but others may simply be victims of misinformation effects on memory, as studied by Dr. Elizabeth Loftus:
4. No black boxes for any of the four planes. Pilots for 9/11 Truth has established that the "Flight 77" black box released by NTSB is not real because the data doesn't match impact with the Pentagon.
5. No debris found below the crash sites or evident in the videos. Wheels and fuselage pieces found beyond the towers on impossible trajectories don't count. No plausible debris for any of the four planes.
(See evidence in argument 2 above, and picture taken by David Handschuh at the Progressive Independent link in argument 3 above.)
6. NORAD/NEADS and FAA confusion about whether radar blips were real or "inputs," with NEADS personnel watching CNN per Vanity Fair. No reason to accuse these folks of complicity.
7. Technological possibility and military doctrine and practice, as discussed in the Washington Post, MIT, and Harvard articles referenced here:
8. Logistical reasons why planes would not be used:
9. Instant media framing of what happened ("collapse" due to plane impact and fire, and "bin Laden did it") as shown by BrasscheckTV:
10. Inconsistent entries in Bureau of Transportation Statistics database:
11. Finally, evidence of faked videos, skillfully compiled in September Clues.
The videos are only part of the argument. To me, the crash physics and the lack of plausible aircraft debris are the most convincing.