The first person to pop into my head would be Micheal Hedges. He used some of the most unique guitar tunings of any guitarist ever, and could literally make you think you were hearing more than one instrument coming from his guitar. He used alot of different tweaks that no other guitarist has ever used before him, not to also add that he was a master shredder and tapper.
Another unique guitarist and unique individual would have to be Buckethead. He is probably one of the best experimental guitarists out there, atleast in the top 3. He can literally recreate all the sounds of a rollercoaster ride and other various park rides from his guitar. He has some pretty awesome bi-dextral techniques. Awesome bass player too.
Another unique guitarist is Jón Þór Birgisson of Sigur Ros. Using a cello bow with an electric guitar to create extremely high-feedback, and put that feedback into very soothing melodies.
I also find Tom Morello to be very unique and widely adaptable. He also has perfected some techniques, one being a scratch technique, that would be considered experimental and make them work in his playing.