The books I have bought most frequently since I keep giving them away to friends are The River Why by David James Duncan, The Phantom Tollbooth by Norton Juster, and Stranger in a Strange Land by Robert Heinlein. But my recommendations always depend upon the recipient.
I see that the two books that stand upon my desk at work and probably won’t ever go away are Additional Dialogue: Letters of Dalton Trumbo 1942-1962, and a second edition of G. Legman’s The Limerick. With a full 1,700 examples in the latter, I never have to reach far for an uplift.
Number 1587:
A bather whose clothing was strewed
By winds that left her quite nude,
Saw a man come along,
And unless we are wrong
You expected this line to be lewd.