Those of you who weren't / aren't gamer geeks may not be aware of a funny little merit of the Dungeons and Dragons character-generation system, which is that one of the attributes you set for yourself is your "alignment," a value that stands in, essentially, for your morality.
I've always liked the way that the alignment system works in Dungeons and Dragons because it's a two-axis system: there's the basic good-to-evil axis that you'd expect, but there's also an axis ranging from "lawful" to "chaotic," which describes your degree of attraction to order. If you were to draw this out as a scatterplot, it would define four major areas, which, in Dungeons and Dragons parlance, are Lawful Good, Chaotic Good, Lawful Evil, and Chaotic Evil.
Last night I saw the new Batman movie (OK, OK, The Dark Knight) and one of the things that I noticed about it is that its major characters align to these four areas. To wit:
Chaotic Good: Batman
Lawful Good: Harvey Dent
Lawful Evil: Two-Face
Chaotic Evil: The Joker
This is not that interesting, in and of itself, to anyone except former gamer geeks like myself, except that it highlights the film's interest in these polarities, in the way that good defines itself against evil, and in the way that order defines itself against chaos. Especially interesting in both Dungeons and Dragons and The Dark Knight is their refusal to conflate good with order and chaos with evil. These pairings can be, and are, often found together (and Heath Ledger's turn as the Joker is nothing if not a memorable embodiment of Chaotic Evil in its most prime manifestation), but they also can be, and are, often decoupled. A recognition of that allows for a more complicated and rich moral universe, and The Dark Knight's exploration of these different configurations is, to my mind, the film's greatest strength.
[A sad closing note: the Wikipedia article on alignment informs me that the new Fourth Edition of the Dungeons and Dragons rules has gone the simpler route, eliminating both Lawful Evil and Chaotic Good. Bloody dualists!]