America the Beautiful - Lee Greenwood, American Patriot

The first, third and fourth verses of this song - particularly the third and fourth - seem to me to speak directly to the event. The lines "whose alabaster cities gleam, undimmed by human tears" is at once a reminder of better times, and also gives a sense that we will not always be brought down. We will not forget, but we can move on to a better place.
And of course, from the third verse: "O beautiful, for heroes proved, in liberating strife; who more than self, their country loved, and mercy more than life" - that line not only speaks of the bravery of our troops, but also of the rescue workers who on 9/11 worked so hard to save people, and who far too often lost their lives doing so.

Anne