Might be nice to find bibliography of some long time published magazine, throw out familiar names and have a brief look at some of those remaining.
During nineties, there was a Czech mutation of Magazine of Fantasy and Science Fiction. It had decades of delay behind the original and was issued bi-monthly instead of monthly so the editor cherry picked from the past and the present of magazine's portfolio. I discovered quite a bunch of interesting names both old and forgotten or new and yet-to-be-recognized, also forgotten faces of familiar names.
Some examples from the magazine would be James Tiptree, Bruce Holland Rogers, Esther M. Friesner, Joe Haldeman (yeah, I've read Forever War and Hemingway Hoax before, but Ma Qui and Graves were different meat), Ray Vukcevich, Vance Aandahl, Barry N. Malzberg, Lisa Tuttle and loads of others I don't even remember, all those authors of twenty short stories and a novel, that somehow made it into publishing three stories in Magazine of F&SF and getting translated 20-40 years later.
As for actual suggestions of forgotten gems or interesting tidbits, there is House on the Borderland by William Hope Hodgson, if you don't mind old fashioned heroes scribbling their Oh No's and God Why's into diary while Unspeakable Horrors enter the door, already mentioned and not exactly forgotten James Tiptree, Jr., non-Amber Zelazny*, Yevgeniy Zamyatin (Us, but his "non-SF" stuff is worth reading too), Kallocain by Karin Boye, William Tenn (Liberation of Earth, Venus and the Seven Sexes), Strugacki brother's (I liked Picnic by the road, but there's more to them, especially "Escape Attempt"), Henry Kuttner/C.L.Moore, Sam Lundwall (No Time for Heroes and Bernhard the Conqueror), Shirley Jackson, Robert Aickman (The Waiting Room).
*Might have been caused by crappy translation but I found Amber books mildly amusing but mostly just fluff, his short stories varying from amusing and interesting to masterpieces; whoever here haven't read A Rose for Ecclesiastes yet and is more of a bookworm with penchant for SF&F instead of die-hard SF fan, go read it _right now_, you won't regret it.