I got the regular (non-classroom) edition of this book as part of the pile of beginner books I picked up when I started uke. I found it to be enjoyable but very basic/beginner. Good for kids or someone who has just gotten a ukulele and has no idea where to start.
21 Songs in 6 Days: Classroom Edition: Student Book
http://www.amazon.com/dp/B01EENWDHQ/
Free through June 6