"This is a series of lessons on Blues Guitar." Simple, but thorough, and with some score/tab as well. Probably worth plugging through.

"Flaming Lips vocalist-guitarist Wayne Coyne brought with him what he dubbed the 'Guitar Hero guitar,' an Epiphone double-neck with the lower, six-string neck replaced by a five-button variant and wired to an oscillator. '[It's] because a lot of kids out there think this is actually the way you play guitar...'" Awesome.

Getting Practice Done. A bit metric/exercise focused for my liking, but maybe worth checking out.

Or, more specifically, a few jazz chords for guitar. Some nice reference on this site, particularly for other tunings such as DADGAD - not the best by a long way, though.

A rather comprehensive history of Hawaiian-style slack-key guitar.