Published and peer-viewed paper "What Did and Did not Cause Collapseof WTC Twin Towers in New York" done by structural engineers. Basically, they are saying that yes, it was the airplanes.
Popular Mechanics also published a book on 9/11. (I may buy it ^_^ Amazon wishlist?)
Skeptic.com (by my idol Michael Schermer) has a comprehensive article about 9/11. The author, Chris Mohr, also has a YouTube playlist to go together with this article, so go check it out!
Finally, confessions of a "Truther" in Cracked.com and I quote: "I cracked and broke down in tears. It was the true human emotion of a mother who lost her kid that changed me. The others believed it was a fake recording and that she was in on it. It was the monstrous ugliness of the other theorists which set me on edge. I'm made to believe they're all a part of the 10,000-man-strong Illuminati? I said to the producers on day five, 'I've changed my mind.'"
Respect victims. The world is not obligated to make sense to you, and have to make you smart and know everything.