The ones I only remember are the Challenger disaster in '86. Sitting in 6th grade the teacher brought the tv in to watch the launch.. boom. ugh.
9/11 I was sitting in my family room with my new born son and was waiting to hear back on a job interview i had a few days before about getting a job. Chills went down my entire body as I watched it. I woke up right at 9:00 and was just in shock the entire day.