I can't decide a favorite book, so I'll just put down a few favorite authors...
Gail Carson Levine
J.R.R. Tolkien (NOT just Lord of the Rings)
William Shakespeare
Gerald Morris
Lloyd Alexander
Shannon Hale
L.M. Montgomery
Sir Walter Scott
Lewis Carroll
Lois Lowry
Elizabeth Marie Pope
C.S. Lewis (NOT just Narnia)
Jane Austen
-Elva