I bought this book a few nights ago:

Music Theory Made Easy by David Harp

because I learned theory quite a long time ago, forgotten quite a bit and picked up bits and pieces since but not really in a cohesive fashion. I figured a quick book might help me better organize and fill in some gaps.

IMO, this book is really good. It will not go into great detail in any form - it's only 80 pages. But it does give you a good basic understanding of scales/chords and their use in rhythm/harmony in rock, blues, country, folk and jazz (not too deep into jazz, though). It uses neither tabs nor notation, but uses primarily numbering (Nashville style) or note letter names. It does not teach any specific instrument. The CD has instruction in one channel and background music to play along with in the other. He calls out chord changes in the music ("four" for the IV, etc).

To keep it simple, there are only 4 chord types that get much discussion - M, m, 7, m7 and 4 scales - major, minor, blues and pentatonic. He explains there are variations of the scales, but only uses the most common. There are several common chord progressions presented. There is a little bit on mixing arpeggio and strums to get the melodic sounding rhythms. It's helping my ear training for chords a lot just learning more common progressions to try. There is a fair amount on using scales to improvise melodies. In the jazz section at the end, he briefly discusses some more advanced chord forms and melodies in scales of more than one key.

Anyway, it is no substitute for an in depth understanding of music, but I think it is a great springboard for people like myself with a limited understanding. It could be frustrating for a total beginner because you need to know a fair number of chords and know how to find notes the right number of intervals away from the root note and play at a reasonable speed.