Reader Mike Felkins sent us an image of the actual Slow Train To Arcturus cover, including the alleged helmet-condom. On the right, the sanitized/misspelled online version. Meanwhile, another site boasts a wealth of bad covers.
Commenter PatZ points us to a site, Punk Rock Penguin, with a shrine of hideously awful book covers, many of which come from science fiction or fantasy. They include some classics (two of the original Dune covers? really?) but also some little-known gems. Here are some of the greatest: