Adams himself wrote five novels in the trilogy(?!) about the travels of earthling Arthur Dent, alien Ford Prefect and others, beginning with "The Hitchhiker's Guide to the Galaxy." It immediately jumped onto my Top 10 list (which, of course, has about 15 entries).
Some years after Adams died in 2001 at the infinitely-too-young age of 49, his widow gave the OK for a sixth book. Eoin Colfer, author of the popular young adult "Artemis Fowl" novels, was beknighted for the infintely-too-demanding task and he added "And Another Thing ..." to the series. It was entertaining enough, and mirrored Adams' twisted humor, but die-hard Hitchhiker fans (like me) did not confuse it with the real thing.
If you've never read Adams' books, pity. These Adams quotes will give you a taste for his style. (And if you have read the books, I'm sure you'll get a chuckle or two from his words.)
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."
"There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened."
"He felt that his whole life was some kind of dream and he sometimes wondered whose it was and whether they were enjoying it."