A couple:
In July 1978 went to a Day on the Green in Oakland, CA. Playing were Aerosmith, Foreigner, Pat Travers and Van Halen. Opening was a relatively unknow "punk-ish" rock band, AC/DC. They came out and literally/utterly destroyed the place. Jaws dropped. Not many had seen anything/anyone like Angus before. The energy was incredible. It was an amazing day.
In July 1982 went to see The Dead Kennedys, Minor Threat, MDC and the Detonators at the Barn in Torrance. Opening was again, a relatively unknown band this time from Indy, the Zero Boys. These kids came out looking kind of dork-ish, (not the typical punk rock "attire" of the day) and just shredded the place from their first song to their last. All bands were exceptional that day, but the Zero Boys blew them all off the stage. They were new, fresh and just a GREAT band. If interested, check out their Vicious Circle LP. One of the best of the genre.