The Lost Princess of Oz, by L. Frank Baum (our reviews)

This rates at the top of the Oz list for me. I enjoyed all the books, but as with any series some will inevitablly be better than others. The Lost Princess of Oz is the tenth book in the series and it brought back every single one of our favorite characters. Calvin loved it. The first few chapters were almost like a roll call and every time another of our best loved friends arrived for the story Calvin would giggle with joy. And we met some delightful new ones, too.