Okay, in roughly chronological order (and my definition of SF is pretty broad here):

Madeleine L'Engle
Ray Bradbury
Zenna Henderson
C.S. Lewis
Mervyn Peake
Pierre Boulle
John Hersey
J.G. Ballard
Harry Harrison
John Brunner
Clifford Simak
Philip K Dick
Larry Niven
Jack Vance
Roger Zelazny
David Lindsay
Marion Zimmer Bradley (I hate to admit it, but it's true)
Poul Anderson
Keith Roberts
Robert Silverberg
Keith Laumer
Fritz Leiber
John Wyndham

...and lots of others, plus a ton of fantasy, but I don't call that SF

Skip ahead about 30 years to my second childhood, and I'd add these as major influences:

Greg Bear
Richard Grant
Tim Powers
Charles de Lint
Gene Wolfe
Jasper FForde
Diane Duane

...and lots of others, again

That was fun! Thanks!