I'll just go with the philosopher who is currently influencing my life today:

Nassim Nicholas Taleb. Black Swan thinking is revolutionary and true, and his lust for knowledge is amazing.

Runner up: Eliezer Yudowsky. Someone who will never stop searching for the truth. Catch his posts at www.overcomingbias.com

(I am biased toward skepticism; there are too many things that have gone wrong by blindly following a school of thought while neglecting what happens in reality.)