Psychic/mind powers just barely beating out necromancy. I love necromancy cause you don't necessarily have to be evil to be one. An honestly good necromancer could be just terrifying if done right.
But I've always been partial to the list of psychic powers. Telepathy, telekinesis, mental persuasion, and mental alteration are pretty much the most basic levels of this and a clever mind can find nearly infinite uses for them.
Read minds to learn secrets, evil plots, true feelings, where something is hidden, etc.
Mental persuasion to convince people to work for you, with you, to turn on their friends, to tell you information, to get what you want, where you want, when you want.
Mental alteration could be a more forceful version of persuasion, or it could be to do the KOTOR thing and completely change the personality.
But telekinesis is probably the most versatile. There's the obvious of just moving things and throwing them, but if you're smart you don't need the dramatic applications outside of probably 1/10 of the time. Subtler movements could be just as effective. A frayed rope pushed past it's limit or a weak link in a chain being exploited could have hugely disastrous domino effects that would be impossible to track back due to seeming entirely mundane.
Or you could use telekinesis to achieve flight by applying it to your own body. Knowledge of the human anatomy could be exploited to cripple an attacker. Of course, the cleverest would figure out exactly how much their ability could effect and how small. IF it were to extend to atomic or molecular levels one could simulate cryomatic, pyromatic, nature based, or earth based powers effectively and efficiently by simply altering the state of the atoms to add or remove heat or "grabbing" objects in the world to fool others into believing it was nature or earth powers.
