The Yes Album.
London Calling.
Although, if only one album would survive the apocalypse, it should be the White Album, because you could reconstruct almost everything else from it.
Led Zeppelin IV
Led Zeppelin IV, by far.
Surprised it got this far without a mention of it. 
Damn, I was beaten. 
Revolver
Exile on Main St. (I have songs I prefer but as an overall Stones album, nothing beats Exile)
Rise and Fall of Ziggy Stardust and the Spiders From Mars
What’s Goin’ On
Sign O’ The Times
Physical Graffiti
I think Blonde On Blonde would have to be right up there.
That’s what I was coming in to say. Otherwise I would pick Sgt. Pepper’s Lonely Hearts Club Band just because of its influence and reputation.
Yep, if I had to pick one. Youth fading fast, fast cars, desperation, love, sex…and what you said !
While I’m at it, I might as well mention the best garage album of all time:
The Sonics: Here Are The Sonics. Twelve songs, less than half an hour, of straight up screaming, blazing punk rock ‘n’ roll. In 1965.
Hmmm. One of the first hard driving rock -n- roll albums that really made me sit up and listen was:
Back in Black - AC/DC – I still think this is one of the absolute best rock albums. Ever.
Diary of a Madman - Ozzy Osbourne – A close second
**
Have Love, Will Travel** flat out rocks.
One of my personal favorites:
From Elvis in Memphis
“Wearin’ That Loved on Look”
“I’ll Hold You in My Heart”
“Long Black Limousine” - George, Stovall
“It Keeps Right on A-Hurtin’”
“Gentle on My Mind”
“In the Ghetto”
The king has spoken. Long live the king.
No question.
The fun thing about these threads is discovering what crappy taste your fellow Dopers have in music!
That is, those of you who don’t have impeccable taste in music.
No, I’m not going to mention names. 
Before reading the thread, I tried to guess what The Answer would be—that is, what albums would be sure to be named, and, if there was any kind of consensus, what it would be. And I guessed that, if there was an answer that most of us could agree on, it would have to be either something by the Beatles (probably either Revolver, Sgt. Pepper, or Abbey Road)), or Led Zeppelin (most likely IV), with possible runners-up by the Rolling Stones and The Who. (I didn’t think of Pink Floyd, but I should have.)
My own personal answer is Abbey Road.
And I pretty much guessed before I opened this thread that there would be multiple mentions of Dark Side of the Moon, LZIV, London Calling, Who’s Next, Sgt. Pepper, and the rest of the Rolling Stone Top Albums usual suspects. In fact, I’m kind of suprised no one has dropped Pet Sounds in here yet.
Most of my favorites have already been mentioned, but I do have one more, which is currently at the top of my list:
The Grateful Dead, American Beauty
If you like American Beauty (as I do, too), you really owe it to yourself to check out Relatively Clean Rivers. To me it’s one of the finest west-coast rural post-60s albums (circa 1975) ever recorded. It’s got a phenomenal story behind it, and the music is absolutely top notch. It doesn’t hurt that it’s got one of the best covers ever, either.
Here’s a few audio samples [WARNING: sound (obviously!)]:
Journey Through the Valley of O
The CD reish has gone out of print recently, but can still be found online. Of course, it’ll probably get reissued again now that Jeff Tweedy has apparently learned about the album and has been dropping its name in interviews…
David Bowie - Ziggy Stardust and the Spiders from Mars