The Phantom Tollbooth, by Norton Juster. A wonderful book, filled with lovable characters and witty wordplay, and it’s spangled with excellent illustrations.
A Whole Nother Story, by Doctor Cuthbert Soup (That’s what the cover says…). Absolutely hilarious. I nearly fell out of my chair laughing. There are two more books in the series, Another Whole Nother Story, and No Other Story. Even kids who don’t like to read may like these. (I know one who loves these.)
The Boxcar Children, by Gertrude Chandler Warner. The books from one through nineteen were really written by Warner, but the rest are obviously mass-produced. The first nineteen are quite good, however the ones after talk down to children.
The Chronicles of Narnia, by C. S. Lewis. The well-known classics, there are seven books in the series. The stories are very inventive, and really show the influence of Christianity on Lewis. Be sure not to buy one of those compilation volumes, as those have smaller print, and cut out some of the illustrations.
And then there are of course children’s editions of The Arabian Nights (make sure it’s a children’s edition), and the usual fairy-tales.
I hope this list is helpful; feel free to comment on it, and offer your suggestions. Thank you!