I remember exactly where I was. Sitting on my dorm room bed, reading Newsweek or Time, avoiding studying. The TV was on, but the volume turned down. I looked up and saw Tom Brokaw talking and wondered what was going on at 2:00 in the afternoon that required him jumping on air. I turned the TV and heard that the world as we knew it had changed. Most importantly, I realized my freshman folly of taking Russian could come to an end: the Cold War was over! I dropped that class the next day.
I would imagine the majority of Americans our age think the most important thing to happen in our lifetimes is 9/11. I understand and respect that view, but the fall of the Berlin Wall was a far bigger event, changing the way roughly 1/4 of the world was governed and altering the way the US looked at the world for threats. With the exception of the odd Romanian dictator and his wife, the revolution was largely bloodless.