The ShortList.com has a post up about the top 50 album covers. Check it out.
From my perspective, there are some sound choices on the list, namely Van Halen's 1984, John Coltrane's Blue Train, Pink Floyd's Wish You Were Here, Rage Against the Machine's debut, and Nirvana's Nevermind.
I know Abbey Road is a classic album cover, and it's on the list, but what about Sgt. Pepper's? That seems like a monumental oversight.
If I were I were to offer other albums and more recent album covers that should be in this conversation, I'm nominating the ones below:
Amanda Shires, Carrying Lightning
American Gun, Therapy
Backyard Tire Fire, Bar Room Semantics
The Bad Plus, Give
Beastie Boys, Licensed to Ill
Death Cab for Cutie, Codes and Keys
Drive-By Truckers, The Dirty South
Faith No More, The Real Thing
Glossary, Long Live All of Us
Jane's Addiction, Nothing's Shocking
Jason Isbell and the 400 Unit
Langhorne Slim & The Law, The Way We Move
Metallica, ...And Justice for All
Police, Ghost in the Machine
R.E.M., Life's Rich Pageant
The Replacements, Pleased to Meet Me
Rollins Band, The End of Silence
Son Volt, Trace
Trampled by Turtles, Duluth
Wynton Marsalis, From the Plantation to the Penitentiary