A tangential discussion of the concept of concept albums started up here in the King Crimson thread. I don't think we've had a thread on concept albums (apologies if we have) and given the musical leanings of members it might be of some interest.
The above discussion landed on the idea that Frank Sinatra is often cited as originating the concept album concept. From what I've read, his 1946 album The Voice Of Frank Sinatra is the one usually credited as the father of concept albums in that it specifically aimed to create a single consistent mood across its tracks and was sequenced so as to have a sustained lyrical flow from one song to the next.
However, others have pointed to Woody Guthrie's 1940 album Dust Bowl Ballads as claiming the title of first ever concept album, being a thematic collection of songs all specifically about the Dust Bowl and its impact on people's lives. Certainly many of the track titles feature the word 'dust' including Dusty Old Dust (the dustiest song title ever?) and, when not mentioning dust, often referencing wind and blowiness. But even the wikipedia entry for that album describes it as "the first concept album, or one of the first" - suggesting there may be other candidates!
Aside from the origins of concept albums, what about the albums themselves, both obvious and less obvious, prog and non-prog? Albums labelled as 'concept' but it's arguable, or those not labelled as such but could/should be?