Dark Roasted Blend has a great article on “pulp” SF magazine and book art, including examples from masters like Frank Kelly Freas and Chesley Bonestell.
They make an interesting point, too:
At the time, the artists working for the pulps weren’t considered anything but cheap creatives providing cheap entertainment for cheap minds. But now we know what they were: visions of wonder, amazing vistas of the imagination, daring dreams of possibility, magnificent views of What Could Be — but most of all we look back at what they did and recognize it for being truly magnificent art.
This is one of the reasons why I have a taste for pulp. The sensawunda just drips from these pages.