The Lord of the Rings, the Silmarillion and the Hobbit are by far my favorite books.
Get "Unfinished Tales" for more Tolkien goodness. It's got some great short stories in it (from all 3 ages). Covers the rise and fall of Numenor (and founding of Gondor) amongst other things.
Oooh and had to mention
John Wyndham. Day of the Triffids. The Crysalids, The Midwich Cuckoos, The Kraken Wakes (this is the exact plot of "X-Com II: Terror From The Deep". I swear the game ripped this Wyndham novel off).
Hmmm I could recommend awesome stuff all day, i'll recommend a couple of less-known authors here, 1960's & 70's sci-fi which I really enjoyed.
John morressey: Frostworld and Dreamfire. A contact story from the alien perspective, seems based on American indian contact with europeans / disease. interesting cultural description and atmosphere. Lots of this authors characters are best described as outcasts, wanderers. Quite a bleak novel, most of his stuff has a similar downer vibe.
Barrington Bailey. "Maths" hard-sci-fi, with reality-twisting brainfuck logic. Fukken Awesome. Surrealist Geek Heaven.
Knights of The Limits was a short story compilation, showcasing the best of his work. unbelievable stuff. Unfortunately I lent this book to someone, then someone else took the book from their house. Grrr...
H Beam Piper. H. Beam Piper ruled ! Too bad he died only 3 years after he started writing novels (he wrote short stories before that).
Which actually says even
more about how good he was, all the novels he produced in those 3 years are pretty good. (He went out the same way as
Robert E Howard, I won't dwell anymore on that)
Philip K Dick. Well, don't need to say anymore about this guy. Won't list the obvious ones, but I quite enjoyed a less-known book by him called "Eye in the Sky"