I figure it's somewhere close to the "official" story, but there are coverups for failing to act in the best interest of our nation. No bombs in buildings, just a lack of action to use the event as an advantage. There were some warnings, and other investigations that were stopped. There were weird stock manipulations, and other small inconsistencies.
The problem is, the conspiracy crowd has littered it (purposefully?) with too much garbage to focus on the little glitches. The little glitches slip through by hiding in plain sight. It's easy to call someone a wacko when they spout the whole line (with hook and sinker) - and point to crappy video's on the web. It's harder to bring up things we forgot, or don't think is as important.
Take nothing for granted, as there are coverups we all see everyday that become news for a day or possibly a week. But don't let strawman arguments take away your rational thought.
EDIT: To Moody Red. "President Bush restored dignity and respect to the White House!" What are you smoking? I voted for Bush, and was severely disappointed!
EDIT2: For the anti-conspiracy crowd, of which I think I'm a part of - Don't use weak arguments like "what happened to the people on the plane" or "how long would it take to wire a building up", or even what you guess might be the number of people involved. You aren't a terrorist (I hope), and you wouldn't know how it was planned - so your conjecture is just as bad.
Lets say the gasmask's dropped down, and instead of oxygen, some other gas knocked nearly everyone out. Then the plane was remotely controlled into it's final destination. That would make a great movie wouldn't it (had 9/11 never happened). Look up the Lone Gunmen, pilot episode, aired in 2000. Chilling to see that again once I got the box set. I had forgotten about it.
Lets say the building needed wiring upgrades, and the PA chose the lowest bidder. Lets say the lowest bidder was a front company, run by who knows who, foreign or not (we have so many illegals here, who know's who's who). They looked like they were installing cisco routers and other cabling, and other wiring to everyone passing by. They had security access to nearly everything at the core. What if the routers and equipment had dual purposes? How many people would it take? Maybe 20 a building? maybe less? What if they were all not US citizens? Arabs overstaying visa's? others? Wouldn't they be able to keep a secret? Sounds like that's out of a movie or Crichton novel too. If you can enjoy a show like 24, this isn't that far off.
I don't believe any of that happened, but it could have - so those are weak arguments. Focus on the rest that makes the "conspiracy" unbelievable. One caveat - I think there might be a case for the plane that was downed over PA, or at least a need for an investigation. Even if it was shot down, it probably was the best thing to do at the time - in light of what happened that horrible day.