Woodstock, definitely. (Gotta kick myself over that one. I was attending college in upstate New York from the fall of 1968 to the spring of 1970, so there's not much excuse for me missing it.)
Beatles at Uline Arena February 11, 1964. (I was 12 at the time and we lived in Northern Virginia. My dad even had an office in downtown D.C. If I'd know and had asked him . . . )
1967 Monterey Pop Festival with The Mamas & the Papas, The Grateful Dead, Janis Joplin, Otis Redding, Jimi Hendrix, Canned Heat, Laura Nyro, Buffalo, Springfield, Quicksilver Messenger Service, Ravi Shankar, Booker T. & the MG's, Hugh Masakela, Jefferson Airplane, The Who, The Association, The Electric Flag, The Paul Butterfield Blues Band, The Blues Project, Country Joe & The Fish.
Nearly any of the Alan Freed shows in the 1950s. See
http://www.alanfreed.com/wp/archives/archives-rocknroll-1951-1959/brooklyn-paramount/