You guys know I'm more of a "Top... List" guy, so I will name some of my favourite albums from the 1990s (a great and an important decade for both Metal and Rock).
Pantera - Cowboys From Hell, Vulgar Display Of Power
Death - Human, Symbolic, The Sound Of Perseverance
Alice In Chains - Facelift, Dirt
Symphony X - The Damnation Game, The Divine Wings Of Tragedy, Twilight In Olympus
Dream Theater - Images & Words, Awake, Metropolis Pt. 2
Judas Priest - Painkiller
Megadeth - Rust In Peace, Countdown To Extinction, Youthanasia, Cryptic Writings
Mercyful Fate - Time (basically their entire 90s run)
KoRn - KoRn, Follow The Leader, Issues
Stone Temple Pilots - Core, Purple
Prong - The Cleansing
Bruce Dickinson - Accident Of Birth, The Chemical Wedding
Corrosion Of Conformity - Deliverance (their entire 90s run)
Crowbar - Odd Fellows Rest (their entire 90s run)
Down - NOLA
Green Day - Dookie, Insomniac, Nimrod
Nirvana - Nevermind
Soundgarden - Badmotorfinger
Faith No More - Angel Dust
Extreme - Pornograffiti
Sepultura - Arise, Chaos A.D.
Suffocation - Effigy Of The Forgotten, Pierced From Within
Bolt Thrower - The IVth Crusade, ...For Victory, Mercenary
Cynic - Focus
Carcass - Heartwork, Swansong
Heathen - Victims Of Deception
Guns N' Roses - Use Your Illusion I & II
Slash's Snakepit - It's 5 O'Clock Somewhere
Van Halen - For Unlawful Carnal Knowledge, Balance
Black Sabbath - Dehumanizer, Cross Purposes
AC/DC - The Razor's Edge, Ballbreaker