National Symphony Orchestra - Children's Series - Fort Meyer Arlington VA, Probably 1956 or 57. The first really moving concert was Glenn Gould at Lisner Auditorium in DC - had to have been 1958 or 59. I can conciously remember Gould and how he horrifed the stuffshirts in the audience.
Hmm from the responses, I guess you're talking about Rock Concerts in which case it would be The Yardbirds' December 23rd show at the Alexandria Roller Rink, in Alexandria VA.