Essential Metal Albums
The following is a list of the essential metal albums. It's official in no way, and feel free to add to the list.
I'll start off with the three "M"s:
Metallica - Master of Puppets
Probably one of the greatest metal albums of all time, Master of Puppets is your first essential. This is easily Metallica in their finest hour and is the same reason why people can hate all their recent stuff yet still consider themselves a fan.
Other high recommendations by this artist:
Ride the Lightning
Kill 'Em All
Iron Maiden - Number of the Beast
Number of the Beast here is also an album of extremely high recommendation. This is arguably Maiden's best work (though I'm more of a Powerslave fan).
Other high recommendations by this artist:
All of their other albums. Seriously.
Megadeth - Rust in Peace
This and Peace Sells are what really make Megadeth so awesome. The other albums are top notch too, but these two stand out as their best. With classic Megadeth songs such as Hangar 18 and Holy Wars, along with my personal favorites Take No Prisoners and Tornado of Souls. The rest of the tracks are top notch as well.
Other recommendations:
Every one of them except for The World Needs a Hero and Risk.
Pantera - Far Beyond Driven
Dream Evil - The Book of Heavy Metal
Kreator - Pleasure to Kill
Judas Priest - Painkiller
Dio - Holy Diver