Sophie's World by Jostein Gaardner
I really enjoyed this one. Clearly a novel for kids, this book provides a nice overview of philosophy. However it is also quite entertaining. Events center around Sophie and her mysterious philosophy teacher. Initially I was disappointed, since it read like a philosophy class given to the reader through letters sent to Sophie, but as the plot thickened, the format changed to socratic dialog.
After a somewhat dry start, it is revealed that in fact the author is himself a fictional character writing a book to her daughter, which reveals a lot of the strangeness that happens in Sophie's World. Towards the end, her world becomes increasingly exciting and fantastical, with cameos from more and more strange fictional characters including Nils and the wild geese. And then it unravels, when Sophie's fictional philosophy teacher reveals to everyone in their world that they are living inside a fiction book. This self-referential trick reminds of Borges and Hofstadter.
I was quite impressed that the Gaardner was able to fit a full intro to philosophy course into a relatively short book, and still make it entertaining. It passed my bar with flying colors and I'm keen to give it to Ben. It can be his high school philosophy class!