Kyuss - 'Blues for the Red Sun'
Queens of the Stone Age - 'Songs for the Deaf'
King Crimson - 'the construKction of light'
Primus - 'Pork Soda' and 'Tales from the Punchbowl'
Amorphis - 'Tales from the Thousand Lakes'
Death - 'Symbolic'
Fantomas - 'Amenaza al mundo' (listening to this can be a hard task for you

) and 'The Director's Cut'
Queen - 'Jazz' and 'Live Killers'
AC/DC - 'Let There be Rock'
Danzig - '4p' and '6:66 Satans Child'
Peter Gabriel - 'Up'
Carcass - 'Necroticism'
Cure - 'Wish', 'Pornography', 'Bloodflowers'
Fish - 'Raingods with Zippos'
Korn - 'Korn'
Lacrimosa - 'Satura'
Megadeth - 'Peace Sells... But Who's Buying?'
Morphine - 'Yes'
Portishead - 'Portishead'
Bjork - 'Vespertine'
Smashing Pumpkins - 'Mellon Collie and the Infinite Sadness'
Type 'o' Negative - 'October Rust' and 'Bloody Kisses'
Nine Inch Nails - 'The Downward Spiral'
Bathory - 'Blood on Ice'
Faith No More - 'Angel Dust'
Soundgarden - 'Superunknown'
Sugarcubes - 'The Great Crossover Potential' for instance

Opeth - 'Still Life'
My Dying Bride - 'Turn Loose the Swans' and 'The Angel and the Dark River'
Gorefest - 'Erase'
Paradise Lost - 'Icon' and 'Draconian Times'
Pantera - 'The Great Southern Trendkill' and 'Vulgar Display of Power'
Slayer - 'Reign in Blood'

hmm... I'm not sure whether it applies, but... John Zorn - 'Naked City'

Rollins Band - 'Weight'
Therion - 'Lepaca Kliffoth' and 'Theli'
System of a Down - 'System of a Down'
Mercyful Fate - 'In the Shadows'
Pro-Pain - 'The Truth Hurts'
Therapy? - 'Troublegum'
Toy Dolls - 'Ten Years: The Best of Toy Dolls'
Nativity in Black - A Tribute to Black Sabbath
Tiamat - 'Wildhoney'
White Zombie - 'Astro-Creep: 2000 -- Songs of Love, Destruction and Other Synthetic Delusions of the Electric Head'
Temple of the Dog - 'Temple of the Dog'
David Bowie - 'Low'
... to name a few.

I hope it doesn't look like the list of my favourite albums. They
are among my favourites, but as n68 said: 'what Rock albums.. they think is a must.. original/ground breaking/qualitywise..', I honestly consider all of them as very valuable for the particular sub-genre or for the rock as a whole. And no, the list is by no means complete.

Happy listening.

edit: formatting