Acoustic guitar is probably my favorite instrument in all the world, and Michael Hedges is one artist who explored the possibilities of this instrument like no one before him. Sadly, he died in a car accident in 1997 at the young age of 43. Fortunately for the world, much of his music is preserved in many wonderful albums, but who knows what might have been had he lived on.
To give you an idea of just how innovative he was, here he is performing the song "Because It's There" (#48 in my list):
Here is Part 4 of a seminar he gave in Pittsburg in 1991, where you can see some of his unusual playing techniques, and hear him talk about Bartok and the Fibonacci sequence:
Michael Hedges Biography
Michael Hedges website with links to Discography, Tunings, Transcriptions, and more.