Good Article on Alter Net
Joshua Holland takes what we might call the Noam Chomsky/George Monbiot approach: That the conspiracy theories distract us from the very real issues, blah blah blah. The actual debunking in the piece is pretty solid, although I had to smile at this:
But asking those questions puts one at risk of being lumped in with a fringe movement, and the result is that we're less likely to get at the truth about what happened that day because of the 9/11 Truth movement, not despite its tireless efforts (a conspiracy theory as good as any other is that the whole 9/11 "Truth" movement is a government operation designed to prevent serious questioning of what led up to the events of that infamous day).
Been there, got the South Park tee shirt.
Hat Tip: Baritone Woman (in the comments), who recommends the comments section on that story for some amusement.