H. Beam Piper's work is free to the public, and available on Gutenberg due to a problem with his copyrights and lack of an heir.
His work in my opinion is some of the best science fiction of that era the golden age. He is in my opinion, on par with Robert Heinlein or Isaac Asimov, except there’s less of his work available because he died in 1963 or 1964.
