9. Darth Plagueis
I actually spent a lot of time wondering whether I should actually add this one to the list: Plageueis's skill with a lightsaber was not the greatest nor was his mastery of the force, but what set him apart from other Lords was that Plagueis was a Sith scholar and a master of midi-chlorian manipulation. Unlike other Sith who desire power above all else, Plagueis desired knowledge: he believed that eventually he would find the knowledge that would allow him to cheat death, a story we hear Palpatine (the apprentice of Plagueis) tell Anakin in Episode III. However Plageuis would never accomplish his goal of cheating death, instead he was betrayed by his apprentice Darth Sidious who proved to be his greatest contribution to the Galaxy.