Here's a few things to keep in mind while picking out harmonica books:
First, it is a really good idea to get a recording to go along with the book, or in the case of ebooks that the recordings are imbedded in the book.
Secondly, don't take a book seriously that says anthing about "instant", "overnight", things like that - it's just not the way the harmonica works - the harmonica is a mouth instrument with no visible moving parts - despite everyone's best efforts, there still will be lots of things that you will have to work out/work on yourself.
Thirdly, a lot of people have trouble beginning to learn to play the harmonica, so if you are one of those people don't feel bad - you are in the same boat with many, no, make that most people, including lots of professional musicians. If you are one of those people then our highest recommendation is Harmonica SuperStart, a proven system that really works for you who want to get started as quickly as possible playing something that sounds good, makes you feel good about your harmonica and feel encouraged to do more.
Fourth: You most likely will want to sample a range of products - each has their own angle and approach and there might be that little nugget in there that is just what you are needing at the time!
Fifth: Listening and/or watching is very important - to keep up your inspiration of course, but also listening is an art form that will teach you a lot about what you are striving for, and watching players live and on dvd is a great thing too.
Bluegrass Harmonica Mike Stevens is a blazing fast Canadian harmonica player - this book is not for beginners (even though it has a beginners section), but it is really good to add actual tunes to your repertoire instead of just blues riffs.