Animals by Pink Floyd. Just a phenomenal photo and totally conveys the bleak theme of the music as well.
Go2 by XTC. My favorite cover ever, completely brilliant.
Year Zero Remixed by Nine Inch Nails. Awesome artwork throughout this project and all the other stuff, especially Ghosts
The Who By Numbers by The Who. The connect-the-dots sketch of the band members is awesome.
Artist: globe (Japan) Album: Lights
from way back. not my favorite but imo best "looking" i've personally seen. i've always liked keiko for her non-jpop idol looks and non-jpop idol voice. too bad the nice cover doesn't justify the remedial music on this album.
Jeeze, of all time? I'm not sure about that right now, but to name some off the top of my head.. You can always count on Radiohead, Pink Floyd or The Flaming Lips having amazing and iconic album art, so anything by them really. I love album covers that feel like accompanying pieces to the music itself, and so that's where my head's at with these choices:
M. Ward's Hold Time
EDIT: Sorry about the size. A tad big. And Kudos to the guys who posted Neon Bible and In Rainbow. Good choices! The In Rainbows art book is amazing as well.