Well, there is the school of thought that says that evil is what evil does, but I don't really buy that. All acts of evil proceed from very natural and good impulses, usually in an incorrect or inappropriate manner. What makes it evil, is like you mentioned, we don't wish to identify with it and push it off to 'other'.
Maybe the closest thing to true evil is impersonal, things like disease and natural disaster. Those things are true 'other'.
Well Fromm, who rejected Jung's thesis of an objective, external evil along with a lot of other ideas as closet theism, suggested that when natural growth and development or impulses where blocked, when good was impossible, the same drives got channelled in an evil way. For instance a sado-masochist is someone whose basic drive for love and relating has been corrupted into coercing and controlling. He had two basic orientations towards existence in his final theory, bio-philis, life orientated, or necro-philis, death orientated, his theory uses the word necrophilis in a different way to it had been previously, its not simply eroticising the dead, so you could prefer objects to people or animals or only prefer people and animals if you can render them into objects, prefering having to being, joy to possessiveness. Sorry, I digress. Anyway, he meant that evil is only human in its origins and abnormal.
While I like Fromm's theories, I still kind of think that Jung's theory of an objective evil makes sense, evil isnt just the abscence of good, that's a little inert and at times evil is really, really proactive and unmistakeable. I cant dismiss the idea of objective external good or evil, as natural forces, like gravitation, as superstition just yet.