I'm still amazed by the fact that no one I knew personally died that day. The closest I could come was, when I worked in Brooklyn, I worked with a young lawyer named Jennifer Glick. Her brother (I think his name was Jeremy) was one of the heroes of Flt 93 who tried to re-take the plane from the hijackers.
Some of the poeple I worked with in Brooklyn were working at 225 Broadway that day, two blocks from the WTC. They were standing in their office kitchen watching the north tower burn when the second plane hit. The fireball was so intense that some suffered the equivalent of sunburn on their faces. Later, they saw the jumpers and even had eye contact with some of them as they fell.
The police had their building cordoned off, weren't allowing anyone to leave, and they were terrified that one of the towers would fall in their direction. One later walked all the way from lower Manhattan to Jamaica, Queens to get a Long Island RR train home.
All in all, I was fortunate. I got to watch from 2 miles or so away.