This review is from: The H. Beam Piper Megapack: 33 Classic Science Fiction Novels and Short Stories (Kindle Edition)
This has so many of his works. Not just his short stories but whole books. It's also in chronological order which is great if you like early 50's si fi.
If you don't already know of H Beam Piper I would really recommend this to get started. His work is also in the open domain so audio is available from librivox.