I'm laughing at the fact that LOTR is far and away the one most listed here; count me in, too.
My favorites are:
Another roadside attraction
Tom Robbins (and all his other books. He has a distinctive, unique and knee-slapping, belly laughing, outrageous and way over the top satire and wit that has reoccurring subjects of religion and spirituality that he mocks and takes seriously at the same time.
the Complete Sherlock Holmes
Sir Arthur Conan Doyle
My first exposure at a young age to logic and rational thinking. It blew me away how he could come up with answers to mysteries by logically deducing them.
Stranger in a Strange Land
Robert Heinlein
I highly recommend this book to all my friends. This is a superb, humorous and insightful look at social issues and religion from "...Within the framework of his science fiction stories, Heinlein repeatedly integrated recognizable social themes: The importance of individual liberty and self-reliance, the obligation individuals owe to their societies, the influence of organized religion on culture and government, and the tendency of society to repress non-conformist thought. He also examined the relationship between physical and emotional love, explored various unorthodox family structures, and speculated on the influence of space travel on human cultural practices."