The soundtrack to "Repo! - The Genetic Opera". Why I like it, I can't exactly say, but it probably has something to do with the guitar riffs used throughout the soundtrack(and in the movie of coruse), and the general "dark" tone of the music(and again, the movie).
My favorite from it would have to be between "Legal Assassin", and "Night Surgeon".
Reasoning for the favorites? Spoiler's abound.
Both of them about the central character from the movie, the first mostly about the fact that he is a dual character, as he fills the role of a Father, and yet, a cold-blooded killer, which, because of the company he works for, it is completely legal for him to do so. And the second, is more about what happened to make him this killer, the death of his wife, (which he was strung along to believe it was he himself, that killed her). Along with this, he fights with the dual personality, even as he walks away, refusing to do what his employer said.