Take a look at this list of new science fiction put up at Project Gutenberg. Lots of familiar (and fairly recent) names there: Philip K. Dick, Mark Clifton, Leigh Brackett, Poul Anderson, Norman Spinrad, Frederik Pohl, and Jack Vance. And the last three of those are still alive.
It would be interesting to know how these slipped into the public domain. Did the original magazines where they appeared use work-for-hire contracts, or did the authors forget to file the copyright renewal?
Edited to add: Wrong link, fixed now.
Edited to add 2: Really, really fixed now. This time for sure!