I'm leaving out so many amazing albums, but these are pretty much "desert-island" choices that I grew up with that still stand the test of time, imho.
In no order:
Black Sabbath - Sabbath Bloody Sabbath (could've gone with any of the first six)
Iron Maiden - Piece Of Mind (could've gone with any of the first seven)
Black Sabbath - Heaven and Hell (gotta have some Dio/Sabbath, Mob Rules a close second)
Motorhead - Overkill (too many to choose from, went with the first one owned)
Ozzy Osbourne - Diary of a Madman (Blizzard a close second)
Saxon - Strong Arm of the Law (other than Armored Saint, the most underrated metal band ever)
Dio - Holy Diver ('nuff said)
Mercyful Fate - Melissa (could've easily gone with DBtO)
Voivod - Dimension Hatross (could've gone with any of their first 6 or 7)
S.O.D. - Speak English or Die 
Feeling slightly gutted that I had to exclude Ride the Lightning, Hell Awaits, March of the Saint, Under the Blade, To Mega Therion.... I could go on and on. Brutal task narrowing down to 10.