@FairWeatheredFriendMany people have mentioned Heinlein and I'll second that. Same for Tolkein. Even if they're NOT your favorite, they're foundational (and, pun intended, Asimov is in there too, especially the Foundation stories).
Stephen King is one of my favorites. I love 'The Stand', warts and all. I'm an enormous fan of the entire Gunslinger saga, up to and including the controversial ending, and works connected to it ('The Talisman' and 'Black House', cowritten with Peter Straub, plus many others). The Bill Hodges trilogy ('Mr. Mercedes', 'Finders Keepers', 'End of Watch') along with 'The Outsider' are wonderful (I'd argue it's really the Holly Gibney series, in the end). 'Eyes Of The Dragon' is short and brilliant. There are some weak King novels (especially when he was really struggling personally), but most are great.
Dan Simmons' Hyperion saga is amazing ('Hyperion', 'The Fall of Hyperion', 'Endymion', 'The Rise of Endymion').
It's hard to go wrong with most of Neil Gaiman's work.
Douglas Adams ('The Hitchhiker's Guide To The Galaxy' and sequels) is well worth your time.
Mark Helprin's 'Winter's Tale' is wonderful, if you like/are willing to try off-kilter 'modern' (turn of the century 1900) fantasy. The movie isn't even vaguely as good as the book.
Three totally different takes on the Illuminati are all a lot of fun: 'The Da Vinci Code' by Dan Brown (which everyone knows, from the movie), 'Foucault's Pendulum' by Umberto Eco (which has the worst opening section of any book I've ever finished - if you slog through the opening, the rest is terrific), and 'The Illuminatus Trilogy' by Robert Shea and Robert Anton Wilson, which is silly-to-ridiculous and is jam packed with both cleverness and idiocy, often in the same sentence.
William Horwood's 'Duncton Wood' series is well worth a look, if fantasy involving anthropomorphized animals is in your space. Think 'Watership Down', but bigger. Much bigger. If 'Watership Down' is 'The Hobbit', 'Duncton Wood' (and sequels) is 'The Lord Of The Rings' and beyond.
I am undoubtedly forgetting some favorites, but that's a whole lot of reading already.