For some reason I like Supertramp album covers. "Crime of the Century" was cool, "Crisis, What Crisis" was somewhat tongue in cheek, and of course "Even in the Quietest Moments" is a classic. I love the piano sitting on a mountain top, with the sheet music open to Fool's Overture. Liked it so much I got the album cover tatooed on my shoulder!
Yes did some pretty interesting album covers, all followed a common look and feel to them. My all time favourite album cover artist was Cal Shenkel, he did some great work on Zappa's albums. Anyone going to nominate Dark Side?