John Brunner
William Hope Hodgson (though I think he's slowly getting rediscovered)
I completely concur with C.L. Moore (haven't read enough Kuttner or "Lewis Padgett" to include them - I didn't think Fury was that great when I read it), Edgar Pangborn, if only for Davy, which is my favourite post-apocalypse novel easily, and Algis Budrys.
On older fantasy - I am only just 40, and I've managed to work back to T.H. White, E.R. Eddison, George MacDonald etc. I think things got worse for fantasy with the predominance of Tolkienesque epic fantasy, but I feel like things are diversified more now, and as long as people like Lovecraft and Le Guin are popular, people will hear about who they like, and will work their way back - in fact, Neil Gaiman is kind of a one-man machine for this, which I appreciate him for. In fact, I picked up on Cordwainder Smith because the collection I looked at had an endorsement by Terry Pratchet on the back of it, now I think about it!
Also
John Brunner
p.s.
John Brunner