I feel like this question is surprisingly hard to answer. I put some ideas down, but don't feel great about any of them...
First, here are some lists: http://en.wikipedia.org/wiki/FP_Top_100_Global_Thinkers
Dragline wrote: Alive -- Daniel Kahneman is the first to mind.
Kahneman - I know he figured out some cool stuff about how your brain works. Great indeed, but maybe Steven Pinker fits better into this list? I thought Joshua Greene's book on the moral implications of cognitive psych research deserves a mention.
Dragline wrote:Botton yes, but only his earlier work. His most recent efforts are not very good unless you really like art.
I liked 'Art as Therapy' and I don't know much about art! I would put him on the list.
I would also put NNT on there. Granted that Mandelbrot got there first, but Taleb got the ideas out there for the public to digest. I have read some of Mandelbrot's general audience writing and think Taleb is better. Not a better thinker, but a better "public thinker" if you will.
I guess my thoughts are around those who have important ideas and are also able to bring them into the public conversation through NPR appearances, NYT/WSJ columns and New Yorker
Others that come to mind for me:
-Susan Sontag would probably make most versions of this list, although deceased 10 years
-David Foster Wallace, in addition to his novels, was an excellent essayist that helps humanize the modern experience a bit