My top twenty favorites are (in no particular order):
The Hobbit by J.R.R. Tolkien
The Lord of the Rings trilogy by J.R.R. Tolkien
The Harry Potter series by J.K. Rowling
The Dune series by Frank Herbert
Quag Keep by Andre Norton
Master of the Five Magics by Lyndon Hardy
The Amber series by Roger Zelazny
Face in the Frost by John Bellairs
The DragonLance series by Margaret Weiss and Tracy Hickman
The Gord the Rogue series by Gary Gygax
The Icewind Dale series by R.A. Salvatore
The Thieves World series - Robert Asprin, Lynn Abbey, and others
The Fafhrd and Grey Mouser series by Fritz Lieber
The Myth series by Robert Asprin
Godstalk by P.C. Hodgell
The Call of Cthulhu anthology by H.P. Lovecraft
The Foundation series by Isaac Asimov
The Guardians of the Flame series by Joel Rosenberg
Cat's Cradle by Kurt Vonnegut
The Hitchhiker's Guide to the Galaxy series by Douglas Adams