Alignment is a touchy issue with some people, more from various DM's dunderheaded interpretations than anything in most rulesets. A while back I proposed my own dunderheaded alignment system based one picking a home team in the great cosmic battle of good versus evil. Here's another alternative.
First, let us begin by assuming that nearly all PCs are Rat Bastards in some way or another. (Do I really need to justify this position? We're talking about a game where core PC activities are tomb-robbing and orc-murdering.) Alignment under this system is determined by the particular manifestation of Rat Bastardliness.
Example 1: Why are the PCs sneaking around a dungeon, killing monsters?
Lawful: Monsters are evil, so sneaking into their homes and slaughtering them in their sleep is completely justified.
Neutral: The bad guys have all this gold. I like gold.
Chaotic: If I killed things back home, I'd be arrested.
Example 2: Having defeated the orc warriors, what do we do with the orc-mommies and orc-babies?
Lawful: Kill them so their orcish evil will not bloom anew.
Neutral: Kill them so none of those orc kids grow up and start looking for vengeance.
Chaotic: Kill them. They go great with potato salad.
Example 3: A kender wants to join the party, should we let him in?
Lawful: Yes, just periodically turn him upside down and give him a good shake.
Neutral: Yes, he'd be great for testing items to see if they're cursed.
Chaotic: Yes, stealing from other party members is a snap when someone else is such an obvious suspect.