P.S. Also, if you suspect that 9/11 was a "false flag operation" and "inside job," the simplest possible conspiracy theory is this:

19 hijackers who were hired by the US government (i.e., they weren't "Al Qaeda operatives") hijacked four planes, three of which hit their targets, and the intense heat of burning jet fuel was sufficient to cause massive destruction and loss of life.

And before you start speculating about "controlled detonation" and explosives secretly planted in the WTC buildings, you need to rule out the above theory -- otherwise, you're just "multiplying entities without necessity."

Similarly, if you think there was a conspiracy within the federal government, you should rule out the possibility of a "Tiny Rogue Cabal" inside the CIA before you start suggesting that the conspiracy went all the way to the White House. (Occam's Razor tells you to prefer a minimum number of conspirators, rather than a huge number of conspirators, since every additional conspirator is an additional traitor or whistleblower or accidental leaker.)

Finally, you need to give some thought to a coherent motive. The idea that Bush planned the 9/11 attacks as a pretext for the invasion of Iraq makes very little sense to me -- since the 9/11 attacks did not use WMDs, yet the justification given for the Iraq War was the supposed danger that Saddam had a stockpile of WMDs. (If Bush planned the 9/11 attacks because he wanted to invade Iraq, why didn't he arrange for some biological warheads or a radioactive "dirty bomb" to be smuggled onto one or more of the airplanes? Or, conversely, why didn't he try to argue that "Saddam is illegally stockpiling X-acto knives and box-cutters"?)

Another line of thought is that the Gummint planned the 9/11 attacks as an excuse to Take Away All Our Freedoms. ("We'll sweep into power with a degree of control that will make martial law look like anarchy" -- Angela Lansbury, The Manchurian Candidate).

Trouble is that such a complete loss of freedom never actually happened. Yes, some aspects of the Patriot Act had the potential to be gradually corrosive of civil rights, and people were quite right to be alarmed that the Patriot Act set "troubling legal precedents." But there's a difference between "gradual corrosion" and the outright suspension of the Constitution. It seems unlikely to me that the Government would go to all the trouble of murdering 3,000 citizens (and temporarily crippling the nation's financial center) as a pretext for passing some laws that were notably NOT very draconian.