Is this meant strictly to be about Progressive Rock album covers, or is this theme not relevant in today's music? If there are more recent examples, I would be interested in knowing (seeing is optional).

This is from Cracked and is totally appropriate for this thread. The rest of their Prog in 5 Minutes article is pretty damn hilarious.

Moontan by Golden Earring. Great album with good cover, but horrifying photo inside the gatefold.

Mmmmm... that's stretching it.