The Stainless Steel Rat books are hardly forgotten. The original trilogy were reprinted by Tor a couple of years ago, and they're all available as ebooks from the SF Gateway. Likewise, the Deathworld books were reprinted a few years ago and are available from the SF Gateway. Then there's the 2000AD comic adaptation, which is available in a trade paperback omnibus.
For truly forgotten authors, how about Francis Stevens, Leslie F Stone, Helen Weinbaum, Leslie Perri, Miriam Allen deFord, Sonya Dorman, Helen Clarkson or Betsy Curtis?