As of now,
bar Maiden... it changes a lot, but these are nearly always there:
Megadeth: RIP and PSBWB
Judas Priest: Defenders of the Faith, Painkiller, British Steel
Black Sabbath: Sabotage, SBS, Master of Reality
Death: Symbolic, The Sound of Perseverance, Human
Nazareth: Hair of the Dog, the debut, Razamanaz, Close Enough for RNR, maybe also Loud and Proud
Atheist: Unquestionable Presence
Genesis: Selling England by the Pound and Foxtrot
Pink Floyd: Animals, WYWH, The Wall and DSOTM
Toxik: Think This
Deep Purple: In Rock (and probably Made in Japan)
Dark Angel: Leave Scars, Darkness Descends and Time Does Not Heal
Roy Wood: Boulders
Anthrax: Persistance of Time and Among the Living
Entombed: Left Hand Path
Rush: 2112, A Farewell to Kings, Moving Pictures... here I'm really not which albums to pick
Pestilence: Testimony of the Ancients and Consuming Impulse
Jethro Tull: Thick as a Brick, A Passion Play, either Aqualung or Minstrel itG
Voivod: Killing Technology and Dimension Hatröss
Led Zeppelin: Physical Graffiti
Motörhead: Orgasmatron and Ace of Spades
David Bowie: TRAFO Ziggy Stardust ATSFM, Low
Dio: The Last in Line and Holy Diver
Miles Davis: Bitches Brew
Gentle Giant: Octopus and Three Friends
George Harrison: All Things Must Pass
Kreator: Extreme Aggression
Bruce Springsteen: The River
Mike Oldfield: Crises, Five Miles Out and Tubular Bells
Cryptopsy: Blasphemy Made Flesh
Thin Lizzy: Jailbreak, Johnny, Chinatown...
The Beatles: Abbey Road, The White Album and Rubber Soul
Immolation: Dawn of Possession
Sparks: The first three albums
The Moody Blues: Days of Future Passed
Suffocation: Effigy of the Forgotten
Emerson, Lake and Palmer: Brain Salad Surgery
Tom Waits: Rain Dogs and Bone Machine
Slade: Slayed?
AC/DC: Let There Be Rock (Australian version - the one with Crabsody in Blue on it)
Evanescence: Fallen (nah, just kidding
)
probably also Metallica: The First Four
In case I was forced to pick only one per band take into consideration only the first album mentioned.