Oh geez, where to start…better break it down by category.
Classic/NWOBHM Metal: Black Sabbath, Iron Maiden, Judas Priest, The Scorpions (up to Love At First Sting, they sucked after that), Motorhead, Saxon, Angel Witch, Samson, Diamond Head, Grim Reaper, many others.
Bay Area Thrash Metal: Megadeth, Slayer (ok so they’re from L.A.), Testament, Exodus, Possessed, Blind Illusion (featuring Les Claypool & Larry Lalonde before Primus!), Death Angel, Dark Angel, Vio-Lence, Forced Entry, etc. Plus the N.Y. scene with Anthrax, Overkill, Nuclear Assault, and S.O.D. Also: Metal Church, Flotsam & Jetsam, Sepultura, Devastation, Laaz Rockit, Assassin, Agent Steel, Steel Prophet, etc. (Metallica may rot in hell for all I care.)
Hardcore/Crossover Punk Metal: Suicidal Tendencies, Corrosion of Conformity, Cryptic Slaughter, D.R.I., Wasted Youth, a few others.
Pop/Glam/“Hair” Metal: yuck, not a lot. Motley Crue started out good, so did Twisted Sister. Dokken, Great White and Skid Row were always more talented and less hairy than most. W.A.S.P. was comical. Quiet Riot, Def Leppard (formerly NWOBHM), even Whitesnake had their moments. I think The Darkness is hilarious. Never could stand KISS.
German/European Speed Metal (aka “Power Metal”): Helloween, Gamma Ray, Blind Guardian, Kreator, Destruction, Running Wild, Evergrey, Pagan’s Mind, lots and lots of others. (DragonForce is just silly IMO.)
Black Metal: Nothing can beat the unholy triumvirate of Bathory, Venom, and Celtic Frost/Hellhammer. (Mercyful Fate too, but they were more progressive thrash.) Never really liked what it became, but some of the freaky bands from Norway (Mayhem, Burzum, Dimmu Borgir, etc.) had some crazy stuff.
Florida Death Metal: Death (R.I.P. Chuck Schuldiner), Morbid Angel, Malevolent Creation, Deicide…never got into this genre much.
Grindcore: Napalm Death, Carcass and Bolt Thrower was as far as I got.
Scandinavian Melodic/Death Metal (aka “Gothenberg” sound): Edge of Sanity, In Flames, Opeth, At The Gates, Katatonia (before they went goth), Tiamat (ditto), Dark Tranquility, Soilwork, Anathema, Amorphis, Dawn…I think I mixed a few other countries in there.
Progressive Metal: Dream Theater (currently my favorite band), Queensryche (until they sucked), Ayreon, Fates Warning, Symphony X, VoiVod, Savatage (the brainchild behind Trans-Siberian Orchestra), Pain of Salvation, many others.
Technical Metal: Not my favorite genre but I like Cynic, Atheist, Pestilence, Helstar, Watchtower, and a few others. Machine Head and Fear Factory kinda sorta fit in here.
Doom/Stoner Metal: Saint Vitus, Trouble, Candlemass, Kyuss (more rock than metal), Pentagram, Sleep, Sheavy, etc.
Viking/Pagan Metal: Bathory (again!), Moonsorrow, Finntroll, Amon Amarth, and a whole bunch of bands whose names I can’t spell.
Nu-Metal/New American Metal: Ugh. Hate this sound. System of a Down was okay. I kinda like Trivium, too. That’s about it.