This is a good idea for a thread, but very difficult. I don’t have a favourite book, or even a favourite author. Also, there must be better books out there that I just haven’t read yet, so I can only comment on those I have. Here is a selection anyway:
People have already mentioned the ‘Dune’ books, Tolkien, ‘Harry Potter’, Orson Scott Card, Arthur C Clarke, Robert A Heinlein and Larry Niven. I second all those, but my favourite ‘Larry Niven’ novels would be ‘Destiny’s Road’ or ‘A Gift from Earth’. Lots of good short stories by him, but ‘The Long ARM of Gil Hamilton’ series, the ‘Flight of the Horse’ series or ‘Inconstant Moon’ would be worth finding. I also like the ‘Man-Kzin War’ books by various different authors.
If you like Harry Potter, try GP Taylor’s ‘Shadowmancer’ and he has a new book out later this year.
If you like Tolkien, try Stephen Donaldson’s ‘Chronicles of Thomas Covenant’. Also any Michael Moorcock, but especially ‘Elric’.
PK Dick has many good short stories. The novel ‘The Man in the High Castle’ is excellent.
Ray Bradbury writes great short stories. HG Wells is surprisingly still good. Apart from those obvious titles by him, try ‘The Sleeper Awakes.’
John Wyndham still holds up. ‘The Chrysalids’ and ‘The Midwitch Cuckoos’ would be my suggestions. Also George Orwell – read ‘Animal Farm’ and ‘1984’.
Anything by Michael Crichton, but especially ‘Jurassic Park’ and ‘Timeline’.
Jeffrey Archer is a good read too, I wouldn’t loan him money, but he can certainly write a good book.
Iain M Banks – all his ‘Culture’ SF is good. ‘Use of Weapons’ I liked best. His non-SF books as Iain Banks are also good. ‘Whit’ is the best of those I’ve read.
Harry Harrison – any ‘Stainless Steel Rat’ book, ‘Make Room, Make Room’ and the ‘Deathworld’ series.
Joe Haldeman – ‘The Forever War’ and ‘The Forever Peace’ (not sequels and both good)
Any of the ‘Flashman’ series by George McDonald Fraser.
Nick Hornby – ‘High Fidelity’ and ‘Fever Pitch’.
Jeff Noon is good – ‘Pollen’, ‘Vurt’ and ‘Automated Alice’. Also William Gibson. I’m just beginning to read Neal Stephenson, but ‘The Diamond Age’ was excellent.
Colin Dexter's 'Inspector Morse' novels.
I read a lot of travel books. Anything by Bill Bryson or Pete McCarthy is great.
I’m sure that I’ve missed loads, but that is enough anyway.