Okay, this is not a list of my favorite fantasy authors, but rather the ones that are my personal biggest influence on D&D/fantasy gaming. The influences on my DMing are more clearcut - I borrow ideas as a player from all over the place.
Well, Ursula K. LeGuin's "A Wizard of Earthsea" impacts my world building to this day, long (loooong...) after first reading it in 4th grade, and rereading it N+1 times since.
Tim Powers, while not writing fantasy, has definitely impacted how I weave plots and mythic-sized secrets into the world. I really like mythic underpinnings to my world and they get worked into the campaign.
Emma Bull's "The War of the Oaks" has absolutely colored how I rung the non-human motivations of fey/elven courts. (Plus inspired PCs and NPCs off Eddi, Pouka, and Hedge.)
Roger Zelazny has provided too many good things to riff off of. Though I'm more likely to steal ideas from works like Jack of Shadows instead of the best known ones like Amber that are too recognizable.
Steven Brust Taltos and Khaven novels have given me more than a few ideas I've pondered that have influenced how I build highly-magical worlds.
Jaqcquelin Carey's various Kushiel books influence how I shape gentle(wo)man rivals/foes as well as the personal nature of politics.
The Knight chapterhouses in Edding's Sparhawk books have added a lot to various guilds I run.
On the player side I've stolen ideas from all over the place. Fritz Leiber, Scott Lynch, David Eddings, Elizabeth Moon (Pak from The Deed of Paksenarrion is hands down my favorite "becoming a paladin" story, Robin Hobb, Guy Gavriel Kay, Walter Jon Williams. And while not an author, a shout out to the movie Ladyhawke because I've tried several times to play a character as glib as Mouse.