Cannibal Corpse - Tomb Of The Mutilated (classic, there are probably better produced and played DM-albums around, but this one's straight and brutal)
Dead Can Dance - Within The Realm Of A Dying Sun (not metal but brilliant nontheless)
Dream Theater - Images And Words (really amazing, DT is far more than a band with only brilliant musicians)
Iron Maiden - The Number Of The Beast (or any of their first seven albums)
Manowar - Kings Of Metal (they're a bunch of posers, but the music's great! "The Crown And The Ring" rules.)
My Dying Bride - Turn Loose The Swans (on of the best and one of the earliest death/doom albums)
Napalm Death - From Enslavement To Obliteration (Scum was great of course, but I like this one even more)
Queensrÿche - Operation: Mindcrime (best conceptual album ever)
Slayer - Reign In Blood (best thrash album ever)
Tristania - Beyond The Veil (best gothic metal album I know, beats anything by Theatre Of Tragedy)