Yep, you struck a nerve. I'm going to invite the conspiracy theorists in to give it a whirl, but first let me ask you something. Please don't waste my time trying to suggest 9/11 was an "inside job" if you can't first qualify yourself as a reasonable and logical thinker by answering this question.

First, and most importantly, I must demand the most obvious thing that any conspiracy, especially on such a large scale, would require: Motive. For an organization as large, wealthy, powerful and globally influential as the U.S. Government is, to go to all the trouble, spending all the time and money and manpower to make something like this happen, there must and will always be a reason. Either something they stand to gain that is worth the cost to gain, or else something they stand to lose that again is worth the cost to protect. Please provide something the U.S. government stood to either gain by orchestrating 9/11, or lose by not orchestrating it. And please make it something more intelligent than "an excuse to go to war". There are plenty of far cheaper and far simpler ways to convince Congress to support a war, and besides, the President can send the Marine Corps anywhere in the world for up to 6 months without waiting for congressional approval... and we can do quite a lot in 6 months. 

Now, with that out of the way I'll address some of the popular arguments. First, the manner in which the buildings collapsed, which I'm sure you've all heard said is "only possible with explosives." Problem with that statement is that it's flat out false. I've also heard that "fire doesn't burn hot enough" to melt the steel and yada yada. 

Where to begin... first of all, with a portion of the building's infrastructure removed, not to mention the considerable damage that can be done to a building with vibration alone (think about earthquakes), and then the significantly higher temperatures that CONTAINED fires (such as in elevator shafts or closed rooms) can reach as the heat continually compounds on itself, and then all the weight that the now-incomplete infrastructure had to support... well, the point is, there were far, far more stressors being applied to that building's support structure than just heat. As for the way they collapsed inward and straight down, that one's kind of easy, frankly I'm surprised none of the conspiracy theorists ever remember this. Architectural Engineering 101. Most modern buildings, particularly in densely populated areas, and especially skyscrapers, are DESIGNED so that in the event of a major catastrophe such as an earthquake, if the infrastructure fails and the building falls, it will be prone to implode and collapse in on itself, thus minimizing collateral damage to surrounding buildings and going down in the "safest" manner possible... just as if it were deliberately brought down by a demolitions expert, who would have the same goal. 

Let's see, what else... to be honest, it's been a while since I entertained a conversation about 9/11, I was beginning to think all the conspiracy theorists had either pulled their heads out of their asses or else simply found something else to dramatize. I don't recall too many of the arguments off the top of my head, so I'll leave it here for now, and add to this as it goes on.