My favorite keyboard player is Keith Emerson (Emerson, Lake and Palmer). His ability to play multiple keyboards and mix music pieces simultaneously are almost unbelieveable. He would stab one keyboard with a hunting knife to hold notes thus freeing up his hands so he could play two other keyboards at the same time. For the grand finale at live concerts, he would strap himself to a grand piano and play while a forklift raised and then rotated the piano (head over heels). The attached link is an example of his insanely fast finger work.
http://www.youtube.com/watch?v=N0FuFfcCZiE&NR=1
Rick Wakeman (Yes) is my second vote getter.