Just finished reading John Connolly's The Book of Lost Things - a fairy tale quest labeled as "for adults," though I think older kids would get it. Good. I enjoyed it. One of the monsters could almost have escaped from Dune, but otherwise it stayed close to classic fairy tale territory. (With a very funny riff on Snow White.)
This book reminded me of another favorite kid-on-a-quest: Summerland by Michael Chabon. More eccentric in its mythologies. Or Neverwhere, a sort of underground/urban version of a magical quest. The monsters in Lost Things were scary, especially the Crooked Man, but I think the trickster Coyote in Summerland is more interesting and, frankly, I vote for the evil duo Mr. Croup and Mr. Vandemar from Neverwhere as Most Likely to Show Up in My Nightmares.
Something about the oily, antiquated politeness of their speech (well, Mr. Croup's speach, Mr. Vandemar doesn't say so much, too busy biting the heads of pigeons) just reverberates in memory.