I talked about one-axis alignment before, and like the concept quite a bit as it makes it easier to pursue a major goal of D&D: men vs. monsters. Some people hate alignments and very few games use them anymore. That kinda sucks. Oddly, most of the online computer rpgs out there have some sort of alignment or faction system, which demonstrates its usefulness in a game. Just another way the "performance art" people have tried to appropriate rpgs, I guess...anyway, here are some alignment systems from other games that I think might be worth porting over to D&D and are worth taking a look at.
This is a natural outgrowth from AD&D, but distills two axes into one:
Chaos - Evil - Neutral - Good - Law
I think this is one of the better possible alignment systems, and I prefer it over the AD&D system for a number of reasons. Evil characters aren't all psychopaths and maniacs, good characters aren't instantly religious zealots. The far ends of the graph are forces of nature, at odds with humanity. My guess is that this is really what Moorcock had in mind when he wrote about Law vs. Chaos; the AD&D system sort of destroyed that concept when it added good and evil to the mix. Most monsters will be Chaotic: outside of human morality, they have no real goals other than wanton destruction. On the other side, a lot of gods will be Lawful: they care only of order and strive to shape the world to their views. This transcends human morality (once again), and is most likely an alien concept to the vast majority of people. Neutrality is essentially apathy, and neutrals just want to be left alone to live their lives. This is dissimilar to AD&D in that it has nothing to do with balance, but a general disregard for the foibles of others. Overall, good stuff.
Another AD&D-inspired system with the concept of neutrality removed entirely. Siembieda almost always includes a paragraph about not allowing neutrals in his games, this being the only "unalterable rule". Don't tell me what to do! Still, he has a good point: people are not neutral. Even in AD&D, neutrality really has nothing to do with individuals, and instead signifies "outside human morality". Forces of nature, animals, faeries, druids, etc. Above I said AD&D uses neutral to denote balance, and that's true if you read the PHB and DMG, but again, extrapolating from the MM and D&DG, it's pretty obvious neutrality isn't meant to be that. My head hurts...
Again, I really like this system. Principled individuals uphold moral codes and always follow the law, unlike Scrupulous ones who are more akin to Charles Bronson. Still good guys, but can use shady tactics. Evil includes the psychopaths and low-lifes, but also the Aberrant characters, the ones who are evil but with twisted moral code of sorts. Dr. Doom is the perfect example: he never breaks his word of honor, follows through with what he says, won't kill innocent people, but is still hell-bent on taking over the universe. A maniac to be sure, but a trustworthy one. The selfish alignments, that's the best part. Two opposite sides of the spectrum, Unprincipled people are generally good but still self-serving, Anarchists are essentially crazy and commit random acts of mayhem but strive to be moral.
My favorite superhero game, the alignment here is super simple: you pick a motivation appropriate to character goals. If he's a hero, you pick a heroic motivation, villains select from the villainous motivations.
Upholding the good
Responsibility of power
Thrill of adventure
It's not hard to figure out what these mean, or how they're played. Batman is seeking justice, Dr. Doom would have power lust. Thrill of adventure is available to both heroes and villains, which is sort of interesting. Not everyone who commits crimes is doing it for nefarious reasons, I suppose. This is definitely a great alignment system for superheroes, but I'm unsure how well it'd work in a fantasy game.
Star Wars (WEG D6)
One of the most straightforward, all PCs are good. That's it. You oppose the Empire and value freedom. However, you can gain Dark Side points for doing evil acts; when you have enough Dark Side points, you become evil and therefore a non-player character. Mechanically, it was advantageous for Jedi to have one Dark Side point as you could never become evil with only one and it gave you an extra die to roll for Force powers. In-game, though, it was a bad idea, like playing with fire. True to the genre, I think for a fantasy game this would work pretty well if you decided to play a game without any fringe characters.
All characters have Stuff, which is essentially a sort of karmic rating system. Characters with a lot of Good Stuff give off an affable air, are luckier, nicer, etc. Bad Stuff characters are rotten, unlucky, menacing, whatever. Zero Stuff was just that: neither. The best part of this system is that Stuff is essentially unlimited, either way. Bad Stuff gives you more points to buy powers, so it's an attractive option. However, Stuff has no relevance to morality per humanity considering Amberites are god-like compared to shadow dwellers. This system would most likely work in a game where character outlook was more important than an overshadowing moral conflict, i.e., probably wouldn't fly in AD&D. If the characters are all deities, though, sure.