I remember a SF book cover with a man looking up at a sky full of floating black rectangular box-like (otherwise featureless) ships. For the life of me, I can't recall what the book was. Anyone recall it?
Possibly The Visitors, by Clifford Simak?
There were editions of both with the same cover art:
Possibly also "2001: Space Odyssey" by Arthur C Clark, or the "2010/2061/3001" sequels. Although in each case I can find, there is only one featureless black monolith on the cover (link to Google image search).