The Rolling Stones
Say what you will about the Stones but they are something else. At one time in the early 70s the Stones were England's largest export, keeping the Crown's central bank from going bust. Now they have played a free concert to one of the largest gatherings of peoples ever. (Less than the death of the Pope though, but how can you be sure of numbers this large without a price mechanism?). I bought Got Live If You Want It at a garage sale as young boy and have kept it ever since.
Mass hysteria, to me anyway, is worth noting. Got Live if You Want It is still my favorite Stones' album, Beggars Banquet a close second.