Ok, had to think about this...
Honorable Mention: 1989-ish: Purgatory , Havoc, and Destructor in Cleveland. The singer for Breaker did vocals for Havoc, one of my all-time fav bands!
5. 1986 - Voivod opening for Celtic Frost. Wow.
4. 1990 - Voivod headlining. Opening acts: Faith No More, Soundgarden - can you believe Soundgarden was the first band on stage?
3. 1981 - Def Leppard opening for Ozzy. "High n Dry" had just come out, & ozzy's first solo tour.
2. 1982 - Iron Maiden opening for Judas Priest - "Number of the Beast" & "Screaming for Vengeance" tours. Holy Crap-a-moli!
1. 1980 - Saxon and Black Sabbath opening for the amazing Blue Oyster Cult! Saxon was almost booed off the stage, had beer bottles thrown at them. They did have guitaers that spun like ZZ Top, only on fire, hah! Sab was amazing, but BOC blew them away. Don;t ask me how, but they did!