Via the BB Submitterator, Boing Boing reader calebkraft says, "I was given several large containers of pulp Sci-Fi publications from the 50s-70s. I've been scanning them and posting at least one a day to the pulp archive. The art is fantastic!"
No kidding. My favorite, among the ones posted so far, is above. Analog, September 1968, Vol. LXXXII, No. 1.
It looks like Analog had a decent budget for art. Their cover paintings are usually fairly detailed and high quality. I'm not really sure what is going on here, but the fantasy fan of me approves of giant marmots that play horn instruments.