Small venue: Savatage and Trouble @ L'amour in Brooklyn, NY, 1990 - both bands at their absolute peak.
Large venue: KISS reunion tour, Madison Square Garden, 1996. I had been too young to see the original four members during their 70s heyday so this one was a long time dream come true.
Others: Megadeth opening for Judas Priest in 1990 (Deth absolutely wiped the floor with Priest that night, which at the time I didn't even think was possible), Type O Negative in 1991 before their first album had even been released, Iron Maiden's "Somewhere Back In Time" tour in 2008, Rob Halford's solo band "Fight" in a tiny little dump bar in Asbury Park, NJ in 1993.
I could go on but those are my faves off the top of my head.
#1 Led Zeppelin- Great Western Forum June 1977- I feel very fortunate to have seen them
#2 KISS- Spring 1976 Anaheim Stadium- KISS might not have been the best musicians but KISS probably put on the best show I have ever seen. Ted Nugent was the band before them . Epic show !
#3 Judas Preist- Spring 1976 at the Whisky a go go- Preist was anything but a household name at this point. They shredded that club ! #4- Van Halen - Great Western Forum Summer 1978- David Lee Roth is hands down one of the best frontmen ever. And these guys had just burst onto the scene at this point !
Rush amazed by Pert's drum set Van Halen (Great party band) AC DC (right after Thunderstruck was released....Always love the cannons) Ted Nugent (He was amazing live) April Wine (anybody remember these guys?)
Ive seen Metallica four times live. each show better than the next. Ive seen Rage Agains the Machine twice, Tool, Godsmack, Soundgarden, Korn, Limp Bizkit, Mudvayne, Filter, Rammstien, Linkin Park, Deftones. there are more but not has heavy as these bands
I guess number 1 for me would be Iron Maiden And Judas Preist at the Providence civic center. Probably 82 or 83? Number 2 would be Motley Crue and Ratt at the Orpheum in Boston. Number 3 a triple bill at the Orpheum with Dokken, Y&T, and Twisted Sister. Number 4 Ozzy with Motley Crue, At the Worcester Centrum. in the same year as #2. Number 5 Ozz Fest with Ozzy Marilyn Manson and Slipknot. Number 6 Monsters of Rock with Van Halen Mettalica Scorpions and others,maybe Helix. Number 7 Y&T at the Channel Club in Boston. Number 8 Van Halen at The Boston Garden in support of Mean Streets. Number 9 Judas Preist With Great White at the Providence Civic Center Number 10 Warrant at the Channel Club in Boston.