The main book I recommend is Guide to Slide Guitar by Warren Haynes. It contains colorful examples that allow the reader to easily learn the technique used by Haynes himself.
In short, he allows the player to play in standard tuning, resulting in not having to detune your guitar just to play a slide, and then walks you through step by step in how to play slides, using riffs he plays as examples - just perfect examples of strum patterns for acoustic guitar.
This book also comes with a cd allowing the purchaser the ability to use multiple media outlets to gain further information.
It is one of the best books on the market, having very high ratings on multiple websites that sell the book and rated anywhere from professional musicians to those who are intermediate level.
The book allows the reader to incorporate the skills in the book depending on which skill level they fall into, with great advice on how to play in general.
The book is a must have for anyone who is wanting to learn how to play guitar and be able to use the slide technique in their playing. The ability to understand the book is all depending on the person reading it, but the examples given made it extremely easy for me to be able to figure it out.
The main thing that sets this apart is the special aspect of the standard tuning which allows the player to play without swapping guitars or retuning their own. There are plenty of slide books out there, but this is one of the few that allows the player to stay in standard tuning.
It is a very good investment for anyone who plans on every playing with a slide technique in their work or for anyone who is interested in learning multiple styles of guitar technique.