I agree with Andwar. There are many pivotal moments in Rock music history in general - Ringo sits in for an absent Pete Best or the chance reunion of Neil Young and Bruce Palmer with Stephen Stills and Richie Furay on the LA freeway in 1966.
I have many personal moments as well. In either 74 or 75, I remember watching the friday night CBS Late Movie which was showing one of Elvis' early films - Jailhouse Rock. I was 11. It was ok but when it came 'round to the title number, I was floored. The choreography was cool but the song itself just seemed right, the complete rock tune. But the sound - the fat, cracking snare and tinkling ivories, the spare but rocking guitar and booming but solid acoustic bass was just tremendous. Scotty Moore, Bill Black, D.J. Fontana and of course Elvis.
Now that's a smokin' rhythm section! Made a huge impression on me.
One of the many favorite live shows (how do you pick?): A crisp Autumn night, senior year 1980. Six of us barreling down I-94 in my buddy's dad's 68 Buick Electra 225 land barge. The sweet smell of... oregano in the air. Destination - the Milwaukee Auditorium to see the Kinks. It was right around the time they released the "One for the Road" live album. We were already huge Kinks fans - Arthur, Village Green, Muswell Hillbillies, Misfits. They played for over 2 hours. Ray Davies and the boys. It was excellent. Full of energy. Great band. I recall Eddie Money may have opened the show though I'd have to check my ticket stub. (Does anybody save their concert ticket stubs?)