The sinking of MS Estonia in 1994. I'm from around these parts. I don't remember it vividly, however, just vaguely.
The major one that registered was 9/11. I was 13 back then. I vividly remember coming back home from school, switching the TV on, and all the channels we had just showing the twins smoking. And our history teacher talking about it to us next day, during the class, explaining things.
Admittedly, I grasped the actual significance of 9/11 only much later. At the time it didn't seem THAT big of a deal. I mean, it was obviously a horrible thing to happen, and I was sorry for all the people who died, don't get me wrong. But I couldn't understand why is the whole world making this much fuss about two buildings in one country.
I didn't understand what it actually meant, America's standing in the world, and the wider repercussions back then.
I still think it's probably the most significant disaster to happen in my lifetime. It changed the world in a lot of profound ways for a lot of people.