My brother-in-law always gets us books for Christmas - so this year I asked if he would get my son a set of Lloyd Alexander's Chronicles of Prydain. This five-book series is a perfect introduction to the fantasy genre, or a good lateral move if your kid (like mine) has already gotten his feet wet with Tolkien.
Based heavily off Welsh mythology, the Prydain books are now in a nice new boxed edition. My son has started on the first book, titled The Book of Three, and is loving it so far. I try not to push books I liked as a child onto my kid, seeing as we're different people with different tastes. I do try to gently nudge, though, and this time the nudging paid off.