I'd put Simak on the list, for sure. City is the one he's most famous for, although Waystation is by far and away my favourite. But then, I rarely run into another Simak fan, so perhaps that's just me...

Memo to self: enlarge Simak collection! (Having lost my previous, large, collection to Someone Who Shall Remain Nameless. (I took almost everything else though, so it's a bit mean me feeling so bitter about the Simak...))