The early pressings of Thick As A Brick, with the complete "newspaper" is another good one. Remember those phony "classifieds"? The same guy's name kept showing up in all of them. Derek Smalls. Wasn't that the name of the bass player in Spinal Tap?
Best album sleeve or album cover? Another good Alice Cooper album is Billion Dollar Babies, which is basically a green foldout wallet with the billion dollar bill inside and the pop out band photos.
As far as the Jethro Tull album goes, maybe that's where Harry Shearer got the name Derek Smalls for Tap! Can't nominate Smell The Glove from Spinal Tap since it's just a pure black cover! In the extras on the DVD they show them doing the autograph session in the record store and they're using black felt pens so you can't even see what they wrote on the album!