Grateful Dead, Blues for Allah
In 1978ish I bought this album based completely on the cover art (I bought and read books using this patented selection method for a while as well). The store I bought it from had a huge poster of the cover in the window which I tried to beg/borrow/buy/steal. No dice. One of the employees probably still has it.

It remains my favourite album/disc by this group and is said to be their finest studio album: jazz fusion meets musical talent. The Dead has put out folk, country, blues, psychidelia, pop...
It took Amazon a whole 2 months to deliver this one. Did they grow the plastic for the disc first?
Edit: make that jazz fusion/psychidelia meets musical talent. The title track starts off using a middle eastern musical scale in and morphs into this psychedelic romp ala early Pink Floyd. How could psychedelia not show up on anything put out by a band that regularly toured on Timothy Leary's magic bus...