Scales and Modes in the Beginning  
Ron Middlebrook
Centerstream Publications
The most comprehensive and complete scale book written especially for the guitar.  Divided into four main sections: 1) Fretboard Visualization, the breaking down of the whole into parts; 2) Scale Terminology - a thorough understanding of whole and half steps, scale degrees, intervals, etc.; 3) Scales And Modes - the rear of the book covers every scale you will ever need with exercises and applications; 4) Scale To Chord Guide - ties it all together, showing what scale to use over various chords.