I found this site from the NY City Fire Department, a tribute to their fallen. Easily, they lost the most men at one time on September 11, 2001. Be prepared to reach for your tissues.
And this, from YouTube:
(I'm not sure why, but I can't get YouTube to embed in my blog anymore.)
On September 11th, we saw the worst that human beings can offer... and we saw the best.
In New York City, we lost police officers, Port Authority officers and other emergency workers, as well as people just going about their lives. In a field in Pennsylvania we lost more people--sons, fathers, brothers, wives, sisters. At the Pentagon we lost still more.