If I had to choose one "essential" album from the artists I believed were the greatest of all time (IMHO) they would be:

Elvis - Aloha from Hawaii
Beatles - White Album
Beach Boys - Pet Sounds
KISS - Alive
Led Zep - 4
Deep Purple - Machine Head
Eagles - Hotel California
Hendrix - Are You Experienced?
Pink Floyd - The Wall
Bon Jovi - Slippery
Cheap Trick - Dream Police
Pearl Jam - Vitalogy
Live - Throwing Copper
Iron Maiden - Number Of The Beast
Jeff Buckley - Grace
Rolling Stones - Tattoo You
Cold Chisel - East
AC/DC - Back In Black
U2 - The Joshua Tree
G N R - Appetite
Springsteen - Nebraska
Scorpions - World Wide Live
Black Sabbath - Paranoid
Van Halen - 1984
Sex Pistols - Never Mind The B*llocks

There are others that will come to me but these will do for starters..... :P