1) The author Eva Ibbotson has written fantastic books about ghosts, witches, wizards, magic, and the sort because "they are just like people but more madder and more interesting" - including Which Witch?, Island of the Aunts, Not Just a Witch, Dial-a-Ghost, Journey to the River Sea, Secret of Platform 13, and on and on...
2) The Phantom Tollbooth by Norton Juster is a classic "children's adventure novel" and "modern fairy tale." The book has been made into a movie, The Phantom Tollbooth, and is a critically acclaimed novel "So many things are possible just as long as you don't know they're impossible."
3) Shel Silverstein's poems - my favorite. My copy of Where the Sidewalk Ends has been read so often that it is falling apart! Pages 39 (Me and My Giant) to 146 (If the World Was Crazy) are no longer attached to the binding, however much I try. My favorite Silverstein poem is "Come In!" (see Welcome, my first blog post). Some of his other books include Falling Up, A Light in the Attic, The Giving Tree (which I think I've read in English, Spanish, and Hebrew at different points)
4) The Magic Tree House Series by Mary Pope Osborne. Magic Tree House Boxed Set, Books 1-4 is the place to start, and once you begin reading, as my little brother will attest to, you just want to keep going! The adventures of Jack and Annie are entertaining and interesting, and they throw some history lessons (albeit unnoticed by the children reading them) into the mix.
5) Andrew Clements' books; Frindle, The School Story, The Landry News, The Report Card, being my favorites. They all revolve around school, so the age-range Clements is aiming for can really identify with the main characters.