Here are some commonly recommended resources in the Theory and Technique Forum. If possible, please see if your question is answered by any of these resources (particularly the online resources) before posting:
Method Books: Fretboard Logic SE-Volumes I and II
Fretboard Logic Volume 3
Fretboard Logic, in short, is a comprehensive resource for Guitar Mechanics, built mostly on the concept of the CAGED Sequence(a great way to get around and understand the fretboard). The third volume expands into music theory as it relates to the guitar, though the first two volumes contain nuggets of such information. As CheshireCat likes to say: "Its not the last guitar book you will ever need, its the first."
Questions about FBL? Best person to ask is CheshireCat.
Online Resources: Chord Progressions Our own CGR creation, this thread is a bunch of chord progressions, and some explanations of why they sound cool. Its worth checking out, it will help you think of music in a different way.
Music theory help.
lots of good instruction here. There is plenty to learn from this site with people to help you out along the way, I reccomend it!
Zentao Guitar
This will teach you everything from the parts of the guitar to sight reading to theory.
Free Online Guitar Lessons
Lots of great guitar lessons; chords, arpeggios, scales, music theory, ear training, techniques, improvisation, reading music, styles, licks & tricks, misc. wisdom, tabs, gear and tech info, power practicing, guitar forums, etc. Everything from beginner to advanced.
Chord-finder
An online tool for looking up how to play chords, or for looking up what chord you're already playing. Comes in a couple of versions, for different kinds of guitars and stuff. Real good tool. Before you ask us how to play a chord, look it up here.
Gear Reviews & News
A rather large archive of instrument and gear reviews.
Have a resource you think should be in here? Send a link and description to one of the mods, and we'll check it out.