The John King "The Classical Ukulele" is a lot of fun, but a little difficult. He arrandeg the songs in a way that subsequent notes of a melody are played on different strings, making the ukulele sound like a harp. It is a bit difficult to play at first, until you get used to jumping back and forth from the A to the G string, but after a little while, it makes the re-entrant My Dog Has Fleas seem to be a wonderful peculiarity of the ukulele. I highly recommend it.
The "Famous Solos and Duets" book is not quite as hard, but just as rewarding. It contains lots of Hawaiian music, and is just very pleasant to play through on a summer afternoon.
Both books contain CDs with John King playing the arrangements in the book, which is worth the price.