OK, I saw this list on Metal-Archives' forum, so not the most original idea but it's fun to do.
First Queen & KISS then AC/DC. But visually & sonically it's unquestionably Nazereth's "No Mean City" LP.
First the Scorpions then to a small degree and much larger degree later on, Judas Priest& Sabbath but more so Iron Maiden circa: "Number of the Beast", mixed in with Ozzy, Dio, & Motorhead.
2nd Def Leppard album (+ all else BEFORE "Pyromania"- the demo, first EPs & the first LP), Saxon & Raven then Blitzkrieg, Diamond Head (via Metallica, Grim Reaper and a ton more later.
Power Metal - 80's style:
Exciter, Helloween, Running Wild, Savatage (up to "Power of the Night" and a little of "Hall of the Mountain King"), Nasty Savage, Heavy Load.
Queensryche, Fates Warning (I avoided both bands after 1988 though), VoiVod - since I didn't get into 'em until "Nothingface". It's rare as fuck that I like anything in this realm nowadays.
Slayer's "Show No Mercy" then about a month later "Kill 'Em All" by Metallica followed a another year later by Exodus' "Bonded by Blood" and the floodgates didn't end 'til mid-'87 when it started really sucking.
1st Wave Black Metal:
Mercyful Fate, Venom & Hellhammer/Celtic Frost + and many years later Bulldozer/Bathory/Destruction/Sodom & recently - Sarcofago
2nd Wave Black Metal:
Satyricon's "Mother North" then the usual of Emperor, Darkthrone (but really got them when they started adding punk in their sound and went back re-reading the interviews to show that they WEREN'T racists or nazis, quite the opposite, Immortal - especially "At the Heart of WInter". (Early) Mayhem & Marduk in recent years
Death Metal - 1st wave
Possessed - Seven Fucking Churches, a bit later Death's "Human",
Death Metal - 2nd wave
Morbid Angel, Entombed, Carcass, Atheist, Dismember, Deicide, Gorguts, Master (though technically they're in the first category).
Grindcore - 1st wave
Napalm Death, Repulsion probably these 2 more than anyone
Bleeaarrrrrgh comp stuff, Spazz, Crossed Out,
Ramones and later The Damned (most of all UK bands), Sex Pistols - though I now think they're pretty half-assed vs. a lot of the better bands around then: Siouxie & The Banshees, The Damned, Chelsea, Buzzcocks & so on...
Crossover/Hardcore - 80's:
D.R.I. - Dealing With It, Crumbsuckers - "Life of Dreams", Bad Brains - s/t ROIR tape, English Dogs, Attitude Adjustment, C.O.C. Later on: The Accüsed, M.D.C., Rudimentary Peni, Subhumans (UK), DKs, Black Flag, and a million more.
Amebix, Meanwhile, Skitsystem, Sunday Morning Einsteins, Ausgebombt, recently: Crude SS & World Burns to Death
Viking Metal - first inklings
Heavy Load (to some degree anyway), Yngwie's "I Am A Viking" (tho' I think that song's really pretty half-assed), 'Maiden's "Invasion/Invaders", Silver Mountain - "Vikings".
Viking Metal - 1990's-now
Unleashed, Enslaved - Momumesion then went backwards into the catalog especially "Eld" and "Frost", Unleashed, Falkenbach, Amon Amarth - up to a point they've started to grate on me lately but maybe it's just their marketing machine than the music.