Many of the works mentioned in this thread are not really obscure.
Here are some obscure ones:
SF: Genius Unlimited - John T. Phillifent
After Things Fell Apart - Ron Goulart
Monument - Lloyd Biggle Jr.
Looking Backward - Edward Bellamy
When They Come From Space - Mark Clifton
The Aluminum Man - G.C. Edmondson
The Ship that Sailed the Time Stream - G.C. Edmondson
The Witches of Karres - James H. Schmitz
Recall Not Earth - C.C. MacApp
The Sky Is Filled with Ships - Richard C. Meredith
Bring the Jubilee - Ward Moore
The Tsaddik of the Seven Wonders - Isidore Haiblum
Fantasy: Lost Continent - C.J. Cutliffe Hyne
Tiger River - Arthur O. Friel
The Pathless Trail - Arthur O. Friel
Hiero’s Journey - Sterling E. Lanier
Gormenghast - Mervyn Peake
Bloodstone - Karl Edward Wagner
Sea Without a Shore / World Without End - Sean Russell
Steel of Raithskar - Randall Garrett & Vicki Ann Heydron
Excaliber - Sanders Anne Laubenthal
Quite so...!
Here are some obscure ones:
Now those are a bunch of forgotten novels! Of the 21 listed, I've only read three (Bring the Jubilee, Hiero's Journey, Gormenghast). Speaking of Gormenghast, did you know there was a 4-hour long BBC miniseries adaptation?