my answer is
When Lee surrendered to end the American Civil War. It was one of the turning points in the young history of my country, but beynod that, Lee was such a genius, and such a proud man, that it must have been one of the greatest acts of courage ever for him to do it.
Of course, I only picked this because I couldn't choose between the hundreds of sporting events I'd like to see, such as the Cubs winning the 1908 World Series, Michigan football winning the first Rose Bowl, or the 11/22/69 game referenced earlier, or the 1980 Miracle on Ice. (I was luckily at the 1994 Miracle on Grass)