Guitar EncycloMedia
This book is a comprehensive presentation of musical thought as it is applied to the guitar. They also offer Fretboard Flashcards, a tool for guitar and 4 or 5 string bass.
http://www.12tonemusic.com/

Quick Start Guitar
A book series for beginners to intermediate.
http://www.quickstartguitar.com/

Serious Guitar
A guitar theory instruction book; by Michael Hoffman.
http://www.seriousguitar.com/

Heavy Guitar Company
Sells Be Dangerous on Rock Guitar, a title on how to become a blues/rock guitarist.
http://www.heavyguitar.com/

Guitar Master
Advanced 3-octave method to improve speed, agility, improvisation, solo playing, and form.
http://www.guitarmaster.net/

Play Guitar by Ear
Self-help guitar book for beginners.
http://www.paperline.com/playguitarbyear/

500 Blues Licks
A book with hundreds of licks in standard notation with corresponding easy tablature.
http://www.laughingraven.com/500blueslicks.htm

Easy Guitar Lesson
Simple method for learning and remembering the basic guitar chord progressions; for beginners.
http://easyguitarlesson.tripod.com/

As-Good-As-It-Gets Guitar Instruction
Sells three books for beginner to intermediate students.
http://www.peak.org/~heartsto/

Roy Chilton Music
Description and order form for Pick guitar, a series of electric and bass guitar tuition books each with an accompanying CD.
http://www.roychiltonmusic.fsnet.co.uk/

Mixta Publishing Co.
Offers a Mariachi method book by a publisher dedicated to preserving the traditions of Mexican and Latino music.
http://www.mixtapublishing.com/

Accompanying Irish Music on Guitar
Frank Kilkelly offers his book and CD, which covers the art of accompaniment, tools for the job and a guide to tunings and styles.
http://www.irishguitar.net/

Easiest Way Guitar Method
Beginners book with 2 CDs on how to play the essential guitar chords and strumming rhythms.
http://www.easiestwayguitar.com

Yellow Guitar Books
Learn how to play method book and 2 CDs, combines theory, fretboard diagrams, and practice plans.
http://www.yellowguitarbooks.com

Accent On Music
Provides instruction books and videos for acoustic guitar which cover alternate tunings, fingerstyle, Leo Kottke, Paul Simon, blues, slide, jazz, and lead guitar.
http://www.accentonmusic.com

Sound Connection
Offers guitar workshop courses, that include both a book and a cassette, by author Ande Flavelle.
http://www.soundconnection.com

Chaz Hart
Classical and electric guitar books, CDs and teaching aids by the artist.
http://www.chazhart.co.uk

Uncle Tim's New eGuitar Center
Offers a series of e-books and audio-visual materials for the beginning guitarist, and those interested in developing technique. Ordering instructions, and online samples.
http://eguitarcenter.com/

Bruce Emery :: Skeptical Guitarist
Presents a series of books on music theory for guitarists, and on playing techniques; includes excerpts, contents, and ordering instructions.
http://www.skepticalguitarist.com/

Guitar-eze
Offers a system based on an alternate tuning, designed to simplify guitar for beginners of any age or musical background.
http://www.easierguitar.com/

Luse Classic Guitar Method
Offers a series of graded guitar tuition books; information about content, and contact details.
http://musicianguitarist.com/

Ted Viera
This jazz guitarist authors a series of three instructional books.
http://www.tedvieira.com

PlaneTalk
This guitar instruction book provides a visualization technique for "seeing" the fretboard, presented in a unique comic strip format.
http://www.thatllteachyou.com/