The Beatles set the bar with Revolver and Brian Wilson and The Beach Boys jumped over it with Pet Sounds.  The Beatles, especially Paul McCartney, were astounded by the album and it helped spur them to their greatest musical achievement.  While alot of people don't consider Sgt. Pepper's as the band's best album, I think the White Album is their best, the ground breaking and influential nature of it can never be denied.  Up to that point, no one thought that a pop album push the boundaries and be a cultural statement.  By creating an alter ego and using a unifying concept of attending a show by the band, the album broke all the rules.  There was not a hit single from the album and the songs merged into one another without distinction.  Even the packaging of the album broke all the rules.  Usually albums were slapped together with little or no thought to the packaging.  The band spend upwards of $100,000. on the album's artwork.  The album's cover stands as pop culture icon on its own and a true piece of art.  It was also the first album ever to contain a reprint of song lyrics.  The songs themselves have almost become irrelevant to the mystique and aura of Sgt. Peppers, but "With A Little Help From Friends", "Getting Better", "Lucy In The Sky With Diamonds", "Lovely Rita" and most notably "A Day In The Life" are classics.