The only real qualification I consider for an album to be "double" is that it comes with two CD's, not LP's. You could technically have two LP's and have the album simply continue onto the other record, but "double albums" usually have full albums separate from each other, either in tonality or lyrical effect. This also means that I do not include "Greatest Hits" albums or collections because that denotes a collection that was most likely not chosen by the artist themselves.
Here are my few favorite double albums:
The Beatles - The Beatles (aka "The White Album")
What does it take to be the biggest band on the face of the planet? Not much if you've already established yourself as The Beatles. The release of The Beatles in 1968 didn't have to capitalize on any of their material prior other than being a double-dose of epic but challenging songs that document the turbulence of the band as well as the culture clash of the 60's. In that regard, both discs contain levels of both loud guitar spectacles and softer balladry, and it makes for an experience rather than an extraction.
The Beatles - "Ob-La-Di, Ob-La-Da"
Bob Dylan - Blonde on Blonde
Bob Dylan - "I Want You"
Led Zeppelin - Physical Graffiti
Led Zeppelin had the early 1970's. Hands down. They took Rock 'N Roll and Blues to places people probably only imagined in their darkest desires. After five hugely successful albums, Physical Graffiti landed and only continued their streak. Every song is in the land of Zeppelin, if a bit more casual that usual, and we're along for the ride cruising down Route 66. It's a fine dose of rock that's unprecedented.
Led Zeppelin - "Trampled Under Foot"
Pink Floyd - The Wall
Pink Floyd's The Wall is a rock opera for the ages. It's also the turning point in Floyd's deep history that began a slow and sure departure of rock greats Roger Waters and David Gilmour. Regardless of the inner struggle, The Wall is so politically punchy and rigid that the songs often fall through the cracks of "the wall" and become stirring masterpieces. It's an experience of epic proportions, maybe a little too much for the time it was released, but it remains one of the most important records in my listening history.Pink Floyd - "Comfortably Numb"
Smashing Pumpkins - Mellon Collie and the Infinite Sadness
We jump ahead to the mid-90's for this shoe-gazing wonder. The Smashing Pumpkins have delved into this kind of territory before, but as a double album, they were able to provide a fully-fleshed spread of emotions. We had a rock record that wasn't so much rock but an escape to the heavens, catapulting the band into the popular conscious forever. Tracks get better with every listen, and it's hard to deny the zest that their signature sound adds to make the whole thing sweeter.
Smashing Pumpkins - "Muzzle"
-DJ