I discovered the following links to some online books about learning to play the Guitar and the Banjo. As a music instructor, I found them very interesting in both how they are structured as well as the marketing of the books with Creative Commons licensing.
If you've always wanted to learn how to play that guitar (or banjo) that's been sitting in the corner gathering dust, check this out:
The How and Tao of Folk Guitar: http://tangiersound.files.wordpress.com/2007/06/folk-guitar1.pdf
If you've always wanted to learn how to play the banjo, here's another link:
The How and Tao of Old Time Banjo: http://www.ezfolk.com/banjo/howtao/