Neil Gaiman - Anansi Boys, American Gods, Good Omens (Co written with Terry Pratchett)
Terry Pratchett - Discworld, Good Omens (Co written with Neil Gaiman)
Dan Simmons - Hyperion, The Fall of Hyperion, Endymion, The Rise of Endymion
Phillip K Dick - Do Android dream of electric sheep? A scanner darkly - the former of which turned into Blade Runner (and is better than it)
Stephen King - Salems Lot, Gunslinger
H.P. Lovecraft - Call of Cthulhu, The Colour out of Space, At the Mountains of Madness - even if some of his writings suffer from extreme moral dissonance today, especially those with any racist undertones, Rats in the Walls for example suffers horribly because Lovecraft calls the main character's cat "****** Man", it turns the entire atmosphere of the piece from being "Supernatural horror with undertones of corruption in the Anglo-american upper classes" into "Lovecraft, stop being a Jerk".
I could go on...