The Advancing Guitarist, by Mick Goodrick
The Advancing Guitarist is a guitar-focused applied music-theory book by jazz guitarist Mick Goodrick. This non-prescriptive book hypothesizes that the first stringed instrument may have been a single-string "unitar", and perhaps we should seek to understand how the first unitarists played their instruments to inform our own modern guitar playing!
The author, Mick Goodrick, is a renowned veteran jazz guitarist. Here's a video of him playing with few other great guitarists at Berklee College of Music in the late 80's:
The Advancing Guitarist encourages aspiring guitarists to take measure of the fretboard and account for all its possibilities, including but not limited to scales, modes, triads, intervals, chords and more. The book also contains some suggested vamps to aid in your modal improvisation practice. A few of these vamps are available on YouTube, if you care to search them out. Here's an example of the F Lydian vamp from the book:
The idea of the unitar is probably what this book is one most famous for, however, it also contains a LOT of other "advancing" material for playing the guitar. Click on the link to the right to purchase it now!