I would definitely have to go with the Wall. It's really hard to do that album justice. Its the concept album to define concept albums. If it was released today, it would probably bomb and then throughout the years become known as a classic. And an album like that will never 1) be duplicated and 2) never experience the cultural and commercial success that it did. And there are maybe 1 or 2 bands out there with the cajones to actually try something like that. The one that I can think of, and this is an easy comparison, is Radiohead. Other then that...I don't know. I mean the guys built a frickin wall ON STAGE when they played it live! The world and fans are way to fickle to appreciate something like that nowadays.
/end rant
2nd would be Rumours...beautiful!
~~Willis