I was at work, I was a telephone customer service rep at American Express then. They have (or had--haven't worked there for years) tvs (mostly used for company announcements) all over the department. After the first plane hit, all of them were turned to the news, so we all watched the second plane hit and everything from then. We had to stay at work in case any of our customers needed us.

I still vividly remember one of the last calls I took that day (because, people had other things to do or concentrate on) was from a gentleman. He noticed my voice was emotional and asked why. I told him. He gasped "OMG, I have people in that building!" and hung up.

AmEx had a travel service office on one of the top floors of the south (I think) tower. Nine of our colleagues died that day. The AmEx home office building is the one you can see in all the coverage with the pyramid shaped top. It was where the flag was hung outside.

I still get very emotional every year on this date.