I've just finished reading Amy King's Spin Control Book. And as a relatively new spinner, I definitely like this book. It's geared primarily towards those spinners with wheels, but the techniques can be converted to those using spindles with a bit of care.
In the beginning of the book, she goes over some spinning basics -- the differences between woolen versus worseted, S-spun / Z-spun, short draw versus long draw, and the different fibers and how they react to certain spinning types. And she has some wonderful color photographs showing how a woolen yarn knit up looks to a worsted spun yarn. In addition, she goes over tips & techniques to help you get your yarn more consistent. She does not go in-depth about some basics, so if you're looking for details, this is probably not the book.
She also goes over plying and the different plying techniques. And again, lots of wonderful photographs showing how a 2-ply or 3-ply pr N-ply does with regular knitting versus cabled knits versus colorwork.
The last few remaining chapters of the book go over the possibilities of what you can do with your handspun, including core spinning, making boucle, and purposefully made 'art yarn'.
The photographs in the book are very well done, and give you a nice view of what can be accomplished and provide a 'guideline' on how things might spin or knit up. The writing style is laid back and easy to read. There's no overly complicated instructions and a lot of the step-by-step instructions are accompanied by photographs.
I have heard that more advanced/experienced spinners might not find a lot of value in the book, but I'd say for beginning/intermediate spinners, this book can show you all of the possibilities and help you get to the next level in your spinning.