THE QUEEN IS DEAD - The Smiths
This is a very good question. Still, through the years I’m still a fan of Little Feat and Lowell George, god rest his soul. So its got to be…Waiting for Columbus.
I have to go with Green Day’s Dookie. I’m a huge Green Day fan so all of my favorite albums are from them.
Paul Oakenfold - Tranceport
Soundtrack to The Harder They Come
Beastie Boys - Paul’s Boutique
Herb Alpert’s Greatest Hits
“Allman Brothers Band Live at Filmore West”
Runners Up
“Atom Heart Mother” – Pink Floyd
“Tadpoles” – Bonzo Dog Band
“The Twelve Dreams of Dr. Sardonicus” – Spirit
“Flash and the Pan”
“John Barleycorn Must Die” – Traffic
“A Night at the Opera” – Queen
“Let the Good Times Roll” – B.B. King
Ella Fitzgerald Sings the Gershwin Songbook. A pure joy. Wonderful song follows wonderful song.
Weird Al Yankovic-“Dare to be Stupid”
For “serious” music:
The Police-“Synchronicity”
The Residents’ first album, Meet the Residents
The Jackson 5’s Greatest Hits
So sue me.
Either 2 Pac: All Eyez on Me or George Strait: Clear Blue Sky
California by Mr. Bungle. The most brilliant album of all time.
Close second… Pet Sounds by the Beach Boys.
I’m still tossing a coin (best out of 999) between:
Van Morrison - Astral Weeks
or
Bob Dylan - Blood On The Tracks
Hard to say, but right now, I really love with my latest purchase, Lara Fabian’s eponymous CD.
Close behind are the soundtracks from Footloose and from South Park: Bigger Longer Uncut.
I’ll second that - possibly the most sing-alongable album I’ve got.
I’ll also nominate London Calling by The Clash.
"Road Apples", The Tragically Hip.
Close runnerup: “Full Moon Fever”, Tom Petty.
Probably #1: Cascade by Peter Murphy.
Runners up:
Substance 1987 by New Order
Fly by Sarah Brightman
Operation: Mindcrime by Queensryche
Pink Floyd “Dark Side of the Moon”. Grew up with it in the cradle, and have listened to it constantly for the last 20 years, it still sounds fresh with every listen…
“Disintegration” - The Cure
“Wish” - The Cure
“Wild Mood Swings” - The Cure
“Bloodflowers” - The Cure
“Second Toughest in the Infants” - Underworld
“Against the Grain” - Bad Religion
“Generator” - Bad Religion
“The Gray Race” - Bad Religion
“Let’s Talk About Feelings” - Lagwagon
“Star” - Belly
“King” - Belly
“Dookie” - Green Day
“Homogenic” - Bjork
“Angelscore” - Chainsuck
“Movement in Still Life” - BT
“Diversions” - Orbital
“Punk in Drublic” - NOFX
“So Long and Thanks for All the Shoes” - NOFX
"Weezer " - Weezer
“Embryodead” - Wumpscut
“Born Again” - Wumpscut
“Music for the Jilted Generation” - The Prodigy
“Big Calm” - Morcheeba
“Nihil” - KMFDM
“Ixnay on the Hombre” - The Offspring
“Peace and Love Incorporated” - Information Society
“Sixpence None the Richer” - Sixpence None the Richer
“Siamese Dream” - The Smashing Pumpkins
“Half Hour of Power” - Sum 41
“All Killer No Filler” - Sum 41
“Karma” - Delerium
“Beyond the Infinite” - Juno Reactor
“Sailing the Seas of Cheese” - Primus
“The Downward Spiral” - Nine Inch Nails
“Afterglow” - Dot Allison
“Earthling” - David Bowie
“Tribal Thunder” - Dick Dale
“Unknown Territory” - Dick Dale
“Mirrorball” - Sarah McLachlan
Oh, did you say just one? 
Doctor Zhivago sndtrack
Titanic and Back to Titanic sntracks
Sheryl Crow, Globe Sessions and Tuesday Night Music Club
Simon and Garfunkel, Parsley, Sage, Rosemary and Thyme
Pink Floyd, Wish You Were Here.