I like a lot of the Hipgnosis stuff, especially if it involves large sculptures or set-ups, usually on albums I don't actually own! And I like the whole packaging of Zep's "In Through the Out Door".
Rush's "Grace under Pressure" is nice to gawp at.
La Bush's "Sensual World" is a lovely pic.
I still really like the old Sisters of Mercy 12" merciful release sleeves.
The Cult - Love
Fields of the Nephilim - The Nephilim
Danielle Dax - Inky Bloaters (Most of her sleeves are quite nice)
A lot of Cope's stuff appeals. I like the Intepreter box with the map and all the other bits n pieces n details you get with his albums. Nice to peruse as you listen.