My first post on Alignment was a rant on how the Alignment system was flawed, but a good step in the right direction deliniating good from evil; or Law vs. Chaos. Since then, an interesting Roleplaying Game had come out that happened to be based on Morte de Arthur back in the early 80s. Yes, I'm talking about Pendragon.
In Pendragon, the most interesting little addition is the Traits and Passions system that is simple enough to grasp for roleplaying morality. Here is how it works:
There are twenty positive traits corresponding to twenty negative traits (i.e. Chaste vs. Lustful and Energetic vs. Laziness). They are on a scale of 1-20, simple enough. Through roleplaying, a trait is challenged, and if a particular trait or it's negative is roleplayed, the trait is checked. After the session, your trait is strengthened or weakened (i.e. if you play a Lustful person, and you don't lust, you check Lustful's opposite -- Chaste) by a value of 1. Traits turn the simple Lawful->Good->Neutral->Chaos->Evil idea into a series of roleplayable traits. Every religion and or Code of Honor, though, champions a set of traits, which is usually five.
Passions, however, represent strong emotions. Hate, Love, Hospitality; these are examples of Passions. The Passion system is also on a scale of 1-20, but there is no corresponding negative traits. Passions are what your character feels. A character can be inspired by his passions or driven to madness by them.
Lets take for example a character with a particular passion: Hate (orcs). What ever the reason why he hates orcs is up to his player (in some regions, though, Hatred is regional). Every time the character sees an orc, he feels his hatred for them. He may be inspired by his Hatred of orcs and use his inspiration as a bonus for attacking them and doing damage. Or, if his hatred is strong enough, he may go mad and start a murderous killing spree of a particular independent orc tribe (like the Frostdragon tribe).
What a wonderful way of roleplaying! Besides the alignment system of D&D or Palladium Books, the traits and passions system is a good way of introducing how to Roleplay morals and ethics to a person. It's a bit gamist, but it inspires roleplaying to a good degree.