Great topic. For mine...
Very Relentless - functionally it was a bit annoying, but as a physical piece housing the booklet and two cardsleeve CDs, rather than just an image... it was amazing, and greater than the sum of its individual parts. Much like the albums themselves, it was both an exploration into new territory, yet at the same time, very Pet Shop Boys. (And as unexpected as this might be in such a topic, I'd like to make an honourable mention also to this bootleg version, which adapted the theme in a more functional manner, but didn't compromise too much on the artistic component)
Disco - something of a strange choice perhaps, but I feel it captures the essence of the release better than any other artwork. Chris, looking cool, potentially providing the 12" music with extra beats and synths in an abstract discotheque setting. And much like many 12" mixes (relative to 7" mixes), it's slightly out of focus, slightly surreal, and challenging to grasp. Never being fully grasped, it maintains its intrigue, decades later.
Being Boring - gorgeous and pure class, just like the song.
Honourable mentions to DJ Culture, Suburbia(Chris)/Catalogue, Actually and Where The Streets Have No Name.
Retro.
