Ask any of your favorite scifi aithors who their favorite scifi authors are and you will come up with:

Cordwainer Smith

Olaf Stapledon

Stanislaw Lem

Phil Dick

Some notables have been mentioned by other posters, let's nod at Aldiss, Sturgeon, Van Vogt, and oh, OK I'll even allow the grand old sacred cows their due, but seriously, folks, if you haven't yet read the greatest of the great, you're stuck in hackland. Find out where all those great ideas were stolen from originally, and check out the above list, conveniently arranged in descending order of greatness.