They don't necessarily have to be good, just anything that's overshadowed by neighbouring titanic releases in a band's discography. In fact, feel free to include some terrible albums that otherwise feel essential for the sake of souvenir or for filling in the gaps of your soul; anything that makes you say 'oh yeah!' and causes you to reevaluate your music encyclopedia which you previously deemed yourself a master at, after years of tediously browsing wikipedia articles of discographies and in turn polluting Microsoft Word with unholy nerdy lists, forbidden to the public.

Here are some of mine.

Echo & the Bunnymen - Don't Let It Get You Down
Television - Adventure
The Stone Roses - Second Album
The Clash - This is England
The Velvet Underground - Squeeze
The Verve - A Storm in Heaven
Morrissey - Bona Drag
The Beatles - Yellow Submarine
The Beatles - Yesterday and Today
John Cale - Music for a New Society
Nicky Wire - I Killed the Zeitgeist
James Dean Bradfield - The Great Western
Siouxsie and the Banshees - Join Hands
Oasis - Whatever
U2 - Rattle and Hum
Pink Floyd - Obscured by Clouds
Kate Bush - Lionheart
Kate Bush - Never for Ever
Smashing Pumpkins - Gish
Smashing Pumpkins - Pisces Iscariot
Black Sabbath - Black Sabbath
Pulp - It/Freaks/Separations
R.E.M. - Chronic Town
Prefab Sprout - Swoon
Cocteau Twins - Garlands
New Order - Movement

Feel free to include rare singles and EPs.