Buckethead -

I personally think he is the greatest guitar player to date -

Heres a video of him playing a solo for nightrain.
He is pure out amazing.

http://www.newgnr.com/dloads/shortclips/bhntrain.wmv

No doubt he is a great guitarist,but the GREATEST is kind of a reach.I would lean more towards someone with more raw emotion and feel to there playing like stevie ray vaughn, joe satriani or eric johnson.(dont forget hendrix or EVH!! long live the greatest guitar player debate :D