Let me see here:
Challenger: sitting in the school gym, with the entire student body, watching the launch as there was a teacher on-board. The teachers all gasped and the TV was shut off and they ushered us all to our rooms ASAP and didn't tell us squat.
9/11: I was in a meeting at work, someone came in and the the twin towers were on fire. We broke up the meeting and went to the cafeteria and turned on NBC. They were talking about the fire, not sure what was going on when we watched the 2nd plane hit on live TV. Spent most the rest of the day watching, including when the towers fell.
Berlin Wall: yes, I remember playing hookie and being at my grandparents when they interupted whatever I was watching with the news the Cold War was over and the wall had fallen. I remember thinking wow, that is kinda cool--look at all them drinking & partying and getting to spray-paint and tear down that wall (I was 13).
realizing that for some reason, things like Di I know about, but I don't have much that was memorable about them. Guess once you start having tons of kids, most of your memories are first words, losing teeth, potty accidents in public, etc.