Some unorthodox picks:
http://en.wikipedia.org/wiki/Stanislav_Petrov (may have single handedly prevented WW3)
http://en.wikipedia.org/wiki/Norman_Borlaug (may have saved over a billion lives due to hunger)
Hitler is obviously there, he INFLUENCED much more of the war than Churchill or Roosevelt, single-handedly.
Most of the list will be filled with dictators, because their influence is much greater than democratic leaders.
Julius Cesar influenced more of history than Silvio Berlusconi ever will... Mao Tse Tung had much more influence over the world than Wen Jibao.
Also the scientists who were "lone rangers" in that they worked from their home, with no major correspondence with others, and made revolutions by themselves.
Newton comes to mind...