The book cover for Naive Set Theory by Paul Halmos is so so good:
The cover is a riff on, I think, Russell's Paradox, a problem with naive set theory described by Bertrand Russell in 1901 about whether sets can contain themselves.
Russell's paradox is based on examples like this: Consider a group of barbers who shave only those men who do not shave themselves. Suppose there is a barber in this collection who does not shave himself; then by the definition of the collection, he must shave himself. But no barber in the collection can shave himself. (If so, he would be a man who does shave men who shave themselves.)
Reminds me of David Pearson's genius cover for Benjamin's The Work of Art in the Age of Mechanical Reproduction.
