I vote Rod Argent of The Zombies
His keyboards make The Zombies, both with his comping and his sick solos.
I like his playing because he's sophisticated and sloppy at the same time. He's got these great licks that you'd hear from jazz guys but he lays it over a real raw track and rushes just enough to give his solos this frantic feel.
I have yet to hear the combination of complexity and soul from another garage rock keyboardist but tell me what you think. I wanna hear about some more players I can check out.
Listen to his organ work on :
Just Out Of Reach (keyboard solo at 1:00)
and then his electric piano work on
She's Not There (solo 1:37)