Terry Pratchett, P.G. Wodehouse, Eva Ibbotson, Christopher Moore, Richard Armour, Douglas Adams, A. A. Milne (his fantasy/fairy tale book "Once On A Time" is especially delightful), Charles Addams, Edward Gorey, Ambrose Bierce ("The Devil's Dictionary"), Victor Borge, Umberto Eco (yes, that Eco - "Foucault's Pendulum" is a hoot!), Crockett Johnson, James Thurber...
I love humor and comedy in most forms.
ETA: If you've ever wondered what would really happen when Superman and Lois Lane finally got together, Larry Niven's essay "Man of Steel, Woman of Kleenex" is hysterical.