60s:
The Beatles / Sgt. Pepper's Lonely Hearts Club Band - it's a cliche, but it changed everything.
The Jimi Hendrix Experience / Are You experienced - blues + LSD = magic.
The Velvet Underground / The Velvet Underground and Nico - there was more to the 60s than flower power. Also a neat distillation of The Factory aesthetic.
The Rolling Stones / Let it Bleed - because the Beatles were losers.
Credence Clearwater Revival / Credence Clearwater Revival - for "Susie Q" alone.
Jefferson Airplane / Surrealistic Pillow - a 60s list would not be complete without at least one album from the bay area scene. This one is as emblematic as any.
Led Zeppelin / Led Zeppelin and Led Zeppelin II - both released in 1969, brought a dark, heavy sexuality to the white-boy blues.
The Byrds / Sweetheart of the Rodeo - country's not just for rednecks.
I know I'm leaving out Motown, The Grateful Dead, Sly & the Family Stone etc. I'm tired and I want to move on.
70s
Black Sabbath / Paranoid - the 60s are over. Rock and Roll belongs to the working class, in this case, ugly guys from Birmingham.
Pink Floyd / Dark Side of the Moon - this could be any of a number of Floyd albums. Dark Side is just too perfect as a symbol of 70s genius and indulgence.
Big Star / #1 Record and Radio City - I call this one album because everybody younger than 50 has them both on the same CD. Take Memphis soul and British Invasion pop sensibility, and mix in a healthy dose of before-its-time songwriter introspection, and you get the greatest album(s) few people have heard (or at least that used to be the case).
The Rolling Stones / Exile on Main Street - again tough to pick a Stones Album, but this perfectly captures the 70s retreat from 60s idealism. Also shows two songwriters at the height of their powers wrestling with their demons for all the world to see.
Various Artists / The Harder They Come Soundtrack - reggae cannot be ignored.
Burning Spear / Marcus Garvey and Garvey's Ghost - emerging from almost impenetrable clouds of ganja smoke, this demonstrates that reggae was as heavy as music could get. Garvey's Ghost is the first (to my knowledge) dub concept album. Like Big Star above, most people probably have both albums on the same CD.
The Sex Pistols / Never Mind the Bollocks . . . Here's the Sex Pistols - if you have to ask why . . .
Talking Heads / More Songs About Buildings and Food - N.Y. art scene freaks, meet Brian Eno. Together, you will make rock as art.
The Cars / The Cars - every song is a delicious, new-wavey treat. Simple pop songs rendered weird and wonderful by the synthesizer.
Bruce Springsteen / Born To Run - Dylan's really from New Jersey, and guess what, he's also a mad studio perfectionist.
80s
U2 / War - Punk made pop? Hard to articulate exactly why this is so great, but it is.
The Beastie Boys / License to Ill - the majority culture can absorp hip-hop, just like the blues. Paul's Boutique is miles better, but this one made everything which came after (both good and bad) possible.
Sonic Youth / Daydream Nation - who knew that something so ugly could be so beautiful.
Public Enemy / It Takes a Nation of Millions to Hold Us Back - finally, music that scares white people (and especially their parents).
Bad Brains / I Against I - hardcore is more than just fast.
This is long enough, I have to get back to work, so maybe more later. Please feel free to rip me a new one.