FWIW... IMO, here's what Rorschach's AL would be:
3.X AL: Lawful Neutral
4e AL: Unaligned.
For 3.X, I'd say Lawful Neutral because he adheres to a personal belief system (the absolute black & white view of the world) and acts accordingly. He wouldn't be good, IMO, because he does things that aren't good to bad people (which, according to his viewpoint, is totally acceptable). It fails to account for the shades of grey common throughlout life, and the very grey area in which he himself operates (which I'm not sure if he's aware of or not—if he were, I doubt he'd have such an absolute black & white about things).
Also I'd argue Lawful Neutral because he's strongly adhering to a personal code, along the same lines as a samurai (whose code may conflict with the local laws of the area he's traveling in, esp. a samurai character in a typical pseudo-European setting—he's following a code, just not necessarily the code used by his local equivalents).
For 4e, I'd say Unaligned, more or less for the same argument. He's not Lawful Good because he does some decidedly non-Good actd, & because he doesn't use the system itself to try to carry out justice (he believes in a code, but not the system).
Then again, a core idea behind D&D is that there are supernatural forces and genuine absolutes of concepts such as "good" and "evil", and the existence of supernatural beings that act accordingly to those absolutes. While it can incorporate the "shades of grey" of the real world ala Unaligned (because, really, that would be the dominant AL IMO), there's the existence of pure good & pure evil in the world (angels, demons, devils, deities, etc.)
(However, keep in mind that even the most powerful beings aren't genuinely flawless & all-powerful—hence the 4e backstory of devils & the like).