via Boingboing, Hedonia has some information about, and images by, Richard Powers, who pretty much defined the look of science fiction book covers in the 1950's and 60's. Powers didn't care much for science fiction himself, but the genre provided a convenient outlet for the kind of images he was interested in making.
I grew up seeing these covers in used book stores. The images that mix default 50's-style ramrod-straight blonde heroes with melting Tanguy-style landscapes especially ring a bell somewhere deep in my hindbrain.