Here is a page on "What I Learned from 9-11 Conspiracy Theories". Some choice bits include:
The U.S. is actually quite popular worldwide; so much so, in fact, that its government must create artificial terrorist organizations to attack it. Left to their own devices, everybody else pretty much respects Americans and leaves them alone.
The WTC towers fell in what was obviously a controlled demolition. The largest, messiest, deadliest, most witnessed, most mismanaged, most ill-timed, most poorly executed, and most uncontrolled controlled demolition in history.
Cries of "Death to America!" and "America is the Great Satan!" by Islamic extremists are all part of our government's plan for world domination. Left to themselves, the so-called "extremists" are actually quite pleasant, simple folk (but very good actors).
If a large, thin-skinned aircraft impacts the side of a thick concrete building at 400mph, and only small pieces of the aircraft are found outside on the lawn, then it's obvious the pieces were planted there, and a plane didn't crash at all.
Because the shape of the impact holes in the WTC towers and the Pentagon don't match what I think the shape of the planes should be, then it must have been some other type of craft that did the damage, in spite of all of the eyewitness reports and physical evidence to the contrary. Which means that, since the alleged hijacked aircraft are, indeed, missing, and the passengers on said aircraft are, indeed, missing, then the government must have landed those passenger jets in secret somewhere, removed the people, killed them, dismembered them, sprinkled their remains around the crash sites somehow, and destroyed/hid the aircraft somewhere else. Masterful. Much more convincing than just actually crashing the planes into the buildings in the first place.
The same nefarious conspirators that pulled off the single largest concerted suicide attack in history forgot to make a hole in the Pentagon to help fake the airliner impact site.