Invitation to a Beheading by Vladimir Nabokov
The funniest book I have ever read -- a surreal book on the absurdity of totalitarianism.
Nine Stories J.D. Salinger
Short Stories are fun. Salinger's are masterful.
The Great Gatsby F. Scott Fitzgerald.
Even though everyone has read it, it still is fantastic.
Arcadia, a play by Tom Stoppard, is really funny, and it is also fun to think about it in the context of Chaos theory and postmodern historiography.
Those are just the tip of the iceberg...reading is pretty much my profession. No one has mentioned the Lord of the Rings, which is kind of interesting, as it is one of the better adventure stories ever written, and Tolkein has certainly played the role of Homer to the modern genre of sci-fi/fantasy.
edit: looks like Braver beat me to it....I had a feeling that it would not take long.