Seems like we tend to think of the bad first...at least I did when I read your ?? (no reflection on you). Sure you already have 9/11, Kenney's assassination, so how about: seeing Haley's comet, the green halo around the sun just before it sets over the Pacific, a flight of a million lady bugs as they lite on your car (happened to my son), the birth of a perfect foal for the first time, or that same foal getting his land legs, the Royal Wedding today (if you are into the Royalty thing), Being at the airport when our troops are escorted thru, seeing people stand and salute, cheer and welcome them home, sitting for hours watching a rose come into full bloom....prob. not what you were looking for...this is just my list, or part of it.
I would say Armistice Day in 1918 (now Veteran's Day) ending WWI, the stock market crash of 1929, Hitler's rise to power in Germany The Dust Bowl The Nazis invading western Europe Pearl Harbor Raising the flag over Iwo Jima V-E Day (Victory Europe Day) V-J Day (Victory Japan Day) First TVs Chuck Berry with Johnny B Goode Elvis Presley's first televised performance JFK assassination the Beatles landing in America the draft of 1968 the ending of Vietnam Watergate Ronald Reagan Berlin Wall Falls First video games (Nintendo)