Given who has gotten in already that shouldn't have, here is a list of some of the many that should get in, in no order.
Megadeth, Slayer, Anthrax, and Accept.
I listen to Megadeth and Anthrax. As a Christian, I'm not a fan of Slayer, however do like Seasons in the Abyss. These artists with Metallica did a lot for thrash/speed metal. Accept- Balls to the Wall, had another song Fast as a Shark that is widely considered a step toward extreme metal.
Scorpions, Motley Crue, Deep Purple, Whitesnake, Dokken, and even Poison should be in. Again given some of the ones in, I could name alot more. I kept out bands in my previous threads. All have had longevity and sold millions of albums.
I will close with acts from or after the 90's. Alice in Chains, Soundgarden, Smashing Pumpkins, Avenged Sevenfold, Papa Roach, Pantera, and Korn. I could add so many others but I will stop here. I don't want to be up all night.