I just encountered by accident a site where I could fritter away hours: Cover Browser, a compendium of "450,000+ covers of comics, books & more". The books section alone is vast, or even just the couple of thousand Dell Books covers, which are generally sensational.
Unlike some publishers of this era, they did mostly manage to drop out of lurid mode for the occasional classics they published, though you wouldn't quite get the flavour of James Blish's Black Easter from this. The cover design is a bit naff but not wildly wrong about the content, but the blurb portrays Blish's tight and theologically literate SF thriller (nuclear Armageddon played out taking the premise that the divine and satanic pantheon exists, and that the magic of mediaeval grimoires works as hard technology) merely as "a novel about black magic" that'll appeal to to readers of Rosemary's Baby. Those readers would also be surprised/baffled by the sparkling literary fireworks of Angela Carter, whose The Magic Toyshop gets the same miscomparison. Logan's Run: good marks apart from the inexplicable nudity of the runners. Brideshead Revisited: some kind of fountaining passion is implied, and the description - "A major novelist's famous best-seller" - suggests the blurb-writer didn't have much idea how to sell Waugh's saga of aristocrats and Catholic angst. Ubik: this is the one Dr C posted a while back, fairly incomprehensile pyschedelia apart from the identifying Ubik spray-can.
I ran into Cover Browser looking for Howard Clewes' novel The Long Memory (Dell cover here). I enthused about the film a while back - see Noir and the North Kent marshes - but just ran into a nice addendum, the full-chapter Google Books preview on the book and film from The cinema of Britain and Ireland (Brian McFarlane, Wallflower Press, 2005, ISBN-10: 190476438X).