I've recently been listening in some detail to the more structurally complex Beatles songs such as Happiness is a Warm Gun and the Abbey Road medley (You Never Give Me Your Money/Sun King/Mean Mr Mustard/Polythene Pam/She Came In Through The Bathroom Window/Golden Slumbers/Carry That Weight/The End). This has been greatly aided by Alan W Pollack's Notes, particularly his very detailed analysis of the Abbey Road medley.
The Beatles really were amazingly disciplined while being amazingly creative when they had their shit together. The Abbey Road medley contains a series of songs (more than just the named ones) that could each have been developed into workable songs in their own right, but the guys were just overflowing with ideas and keen to try new forms after all the years of fairly straightforward songwriting.
Paul's inherent sense of the catchy tune coupled with John's playful technical and structural hacks just blow me away. Every additional listen brings out new details. This may seem a rather academic exercise but I would recommend it to any music lover, particularly those who like music with deep structure but appreciate pop.
Next one to look at will be Paul's Boutique by the Beastie Boys, possibly the best hip-hop album ever. For this I will be aided by Brad S Benjamin's excellent analysis.