Webby already posted "Who Killed Amanda Palmer" so er hum.
Also do love the art for Tool's "Lateralus"... multitude of fold-out pagesleaves me with no other comment than "ooh, pretty."
Tried to avoid the ones that I just like through familiarity, such as David Bowie, blink-182 etc
So, er, um, here's a few off the top of my head that I quite like.
The Tubes' self-titled album:
I do like Absentee's album and single art:
Half Man Half Biscuit get a mention, for the album names if not the designs.
Also there's an obligatory James posting.
Aside from "Laid", which is pleasantly ridiculous, I like "Pleased To Meet You" as it's a composition image of all of the band members' faces.
Yes, I'm 20 and still impressed by photoshop.