..these are the results:
As far as I know, one man is responsible for all of these. I shall not include his name or the titles of the books in the text here, as I fear him stumbling upon me. Also, from his site, he seems an awfully nice chap, and I feel bad about the sneering (though obviously not enough to not do it). And if that last cover isn't making use of a photo of Indiana Jones then I'll eat that hat.
UPDATE: Readers, I ate that hat. Sharp-eyed commenter Kim Senior points out that the cover in question actually knocks off this Humphrey Bogart image. The trenchcoat should have tipped me off.