That's a good one and there are lots of others among the classics, "The Stranger," "Bartleby," "The Great Gatsby," and "Silas Marner." (I didn't like Gatsby, but most people seem to love it.)
A few not *too* recent short books I highly recommend are:
"The Cambridge Quintet," by John Casti. (historical fiction)
"Four Plays by Karel Capek"
"The Flanders Panel," by Arturo Perez-Reverte. (fiction)
"Enigmas of Chance," by Mark Kac. (Autobiographical)
Rather than focus only on the short book, one might consider expanding into the short stories. I like to keep collections of short stories and poems within an arm's reach of anywhere I spend a lot of time. So I have Rubaiyat next to one tube at home, collection of american poems next to another, book of american short stories next to my bed (along with a biography of Alan Turing). Other than science fiction, I really didn't care that much for short stories until fairly recently. A very few that I highly recommend are: Rothschild's Fiddle and Grasshopper (both by Chekhov), Harrison Bergeron (Vonnegut), and "Outcasts of Poker Flats" (Harte?). It's nice to have collections of people like H.H. Munro or O'Henry just sitting around, gathering dust but for the infrequent scrutiny.
I used to have this teacher who always said, "No intelligent person is ever bored." It's taken me a long time to come around, but I find that I almost believe this sentiment that formerly seemed so absurd to me. I think maybe intelligent people have interesting books in conspicuous places, and scraps of paper and pencils stuffed into crevices but generally within arm's reach.
k
