David Eddings
(1931-2009) is one of those authors who first got me into fantasy literature. I always thought he was underappreciated as an author. His books were light and fun, but they were a tremendous amount of fun. I have read three of his series, The Belagariad which introduced us to Garion, Polgara and Belgarath, The Mallorean which is a sequel to the series, and the Elenium which is a different trilogy.
Before Harry Potter these books were probably the best Young Adult type books available to get kids into reading. There are so many of my nieces and nephews that I have given these books to who are now hard core readers.
Another very interesting book he wrote was The Rivan Codex
. Actually I am thinking of the introduction to that book, but for anyone who wants to read about how to go about writing a Fantasy book its an invaluable tool, with excellent insights into the process.
UPDATE: Tor.com has a great tribute.