An easy pick for me but it captures the last decade so well. Lincoln looking at the noose/halo is what sends this one over from being just a funny picture into being genuine art. It should be in a gallery. It should be in the entryway to the White House.
Some musicalization for this era defining photo: Le Temps des cerises
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy: