This was our era's Reichstag Fire.
After reading the responses, and being asked privately, "Does that mean you're a 'truther'?", I feel the need to restate this more clearly:
The events of 11 September 2011 more closely resemble the Reichstag Fire than Pearl Harbor, most significantly in our response to them as a nation.
Certainly, it is not a one-to-one congruence -- but the "Pearl Harbor" comparison is bandied about far more often, with few objections, and the correspondence is no more exact.
The sticking point for most respondents seems to be the identity of the perpetrators of the Fire. That's a niggling detail, irrelevant to the thesis. I find the nature of our national response to be a matter of far greater importance, because we, lashing out in terror for a decade, have done far more damage to ourselves, to our freedoms, and to the world than the people in those planes ever could have.
The Most Significant Point of Similarity is not whether or not it was an "inside job", but in the fact that it allowed the ugly strain of authoritarianism that had been seeping into into our national political culture for years to finally consolidate its power and win the hearts and minds of the public.
If you want more discussion of "the nature of our national response", feel free to consult Mr. Hicks for his opinion thereon.