Science fiction, fantasy, and horror movies were a big influence. In fact, all of us tend to get ample helpings of fantasy when we are very young, from fairy tales such as those written by the Brothers Grimm and Andrew Lang. This often leads to reading books of mythology, paging through bestiaries, and consultations of compliations of the myths of various lands and peoples.
Upon such a base I built my interest in fantasy, being an avid reader of all science fiction and fantasy literature since 1950. The following authors were of particular inspiration to me. In some cases, I cite specific works, in others, I simply recommend all of their fantasy writing to you. From such sources, as well as just about any other imaginative writing or screenplay you will be able to pluck kernels from which grow the fruits of exciting campaigns. Good reading!
Anderson, Poul. Three Hearts Three Lions; High Crusade; Broken Sword
Bellairs, John. The Face in the Frost
Burroughs, Edgar Rice. "Pellucidar" Series; Mars Series; Venus Series
Carter, Lin. "World's End" Series
deCamp, L. Sprague. Lest Darkness Fall; Fallible Fiend; et al.
deCamp & Pratt. "Harold Shea" Series; Carnelian Cube
Farmer, P.J. "The World Of Tiers" Series; et al.
Fox, Gardner. "Kothar" Series; "Kyrik" Series; et al.
Howard, R.E. "Conan" Series
Lanier, Sterling. Hiero's Journey
Leiber, Fritz. "Fafhrd & Gray Mouser" Series; et al.
Merritt, A. Creep, Shadow, Creep; Moon Pool; Dwellers in the Mirage
Moorcock, Michael. Stormbringer; Stealer of Souls; "Hawkmoon" Series
Offutt, Andrew J., editor Swords Against Darkness III
Pratt, Fletcher. Blue Star; et al.
Saberhagen, Fred. Changeling Earth; et al.
St. Clair, Margaret. The Shadow People; Sign of the Labrys
Tolkien, J.R.R. The Hobbit; "Ring Trilogy"
Vance, Jack. The Eyes of the Overworld; The Dying Earth; et al.
Zelazny, Roger. Jack of Shadows; "Amber" Series, et al.
The most immediate influences upon AD&D were probably deCamp & Pratt, REH, Fritz Leiber, Jack Vance, HPL, and A. Merritt; but all of the above authors, as well as many not listed, certainly helped to shape the form of the game. For this reason, and for the hours of reading enjoyment, I heartily recommend the works of these fine authors to you."
-- G. Gygax, Appendix N, 1979 AD&D Dungeon Masters Guide, p. 224