Bad Brains

Iron Maiden, Saxon, Motorhead, and Black Sabbath.

Anthrax

Dio

Slayer

Rainbow

Megadeth

Misfits

Iron Maiden

Bad Religion

Slayer

Misfits

Black Sabbath

Faith No More

Fugazi

I could go on but from you list, those come to mind

Rainbow (and Dio), Danzig, and Korn. Disturbed and Godsmack also go hard as fuck.

Just to add some I don’t see already mentioned:

Opeth, Anthrax, Kreator, Rammstein, System of a Down, Static X, In Flames

Anvil deserves to be on this list.

Sepultura and Sarcófago

Nightwish

Candlemass

Crypta (They’ll be considered classics when enough time has passed IMO).

Pantera

Exodus

Megadeth

Fear Factory

Napalm Death

Less known band, but I head banged hard to Accept in my teen years for a short spell. Balls to the Wall was their big single but I remember liking most their stuff short a short time.

I’ll add a few.

Death

Pentagram

Atomic Rooster

Cirith Ungol.

Depends on how you define classics, but Sabbath is a must listen, in every incarnation they’ve had.

I’d suggest Deep Purple as well, maybe some Steppenwolf and Iron Butterfly

You’ve got bands like Maiden that you have to listen to at least once. Judas Priest is in that category as well, imo.

If you like thrash, then try some exodus, anthrax, megadeth, overkill, kreator and testament

Sepultura is kinda like pantera in that they blend genres a lot, and both are kinda central the the post-80s metal wave.

Fucking motorhead. That’s all that needs to be said

Saxon is a cornerstone band. Nwobhm wouldn’t have been the same without them

If you want darker/heavier stuff, Death is often cited as the forefront of death metal (though I don’t agree). Cannibal Corpse goes back a ways far enough to be a classic band. Dimmu Borgir for the blacker side of things, and I think if you like Bathory, you’ll love Dimmu Borgir.

Fuck, I can’t not recommend Amon Amarth. Fucking gods of metal.

I’m trying to stick to stuff that’s been around long enough to be considered classic, and is also fairly accessible in terms of how far down the rabbit hole you’d be climbing. There’s a lot of bands that are essentially formative to one subgenre or another, but don’t really hit for most people, or are hard to find to listen to.

Hell, you’ve got stuff like burzum that essentially founded a subgenre, but kinda suck enough that even some fans of that subgenre don’t really listen to more than once.

But, yeah, it really depends on what kind of “classic” you’re looking for, and whether you want the stuff that tends to be widely loved, or a more niche experience.

Some unmentioned: Darkthrone, Emperor, Blood Incantation, Sleep Edit:Blood Incantation is relatively new

Killswitch Engage

Avenged Sevenfold

SOAD

Five Finger Death Punch

Bullet For My Valentine

Children of Bodom

Slipknot

Lamb of God

Morbid Angel - Altars of Madness

Carcass - Necroticism

Darkthrone - A Blaze in the Northern Sky

Exodus - Bonded by Blood

Dark Angel - Darkness Descends

Atheist - Unquestionable Presence

Beherit - Drawing Down the Moon

Gorguts - The Erosion of Sanity

Iron Reagan - Crossover Ministry

Ripping Corpse - Dreaming with the Dead

Necrophagia - Season of the Dead

Vektor - Black Future

Aura Noir - The Merciless

At the Gates - The Red in the Sky is Ours

Kreator - Pleasure to Kill

Sadus - A Vision of Misery

Testament - The Legacy

Destruction - Infernal Overkill