Sometimes fighting evil....
The campaign I used to run we usually didn't use alignment for the characters and NPC's, this allowed our game to be more ambivalent, so that a power struggle between the church and the state could be played out in realistic machievellian terms. Classes, like paladin were held to their code of conduct.
The main thrust of the game iwas a pollitical power struggle in a crumbling, decadent empire. Forces from within and without are trying to gain the upper hand while forces in the government struggle to stay on top of it all (and they aren't even necessarily the good guys!). These were the main factions:
The Kith Roi (Think Jack Nicholson from A Few Good Men: "I have neither the time nor inclination to explain my actions to a man who sleeps and rises under the very blanket of freedom I provide and who questions the methods I use to safeguard those freedoms...). The Kith Roi, translated Crown's Brothers, are the secret police who protect the realm and seek to out maneuver the others. Their principle tools are assisination, political manipulation, and intimidation. The Roi are the true power behind the throne, and the king is part and parcle a member of their organization. It is an organization filled with both Paladins and assasins, although there is equal representation of all classes.
Sons of Mythonius (An underground religious organization carrying out its own inquisition.) Aelfric Mythonius was a Church inquisitor who carried his inquiry to the foot of the throne and whose order was decimated for it. Their libraries filled with esoterica were put to the torch, their members burned at the stake, for crimes of heresy, necromancy, and .... worse. Over time the Sons appropriated the methods of those they hunted. Most notably their use of the undead, who they preach work of years in Purgatorio by serving the order. They are the closest thing to true good guys the campaign has, although their methods are suspect. Mostly wizards and clerics.
The Fiona (Ethnic seperatists, revolutionaries) The Empire actually straddles several ethnicities. One of those ethnicities wants out and the Fiona are their revolutionary arm. All classes though mostly rangers, druids, and rogues.
Society of the Common Meal (Anarchists, radical revolutionaries) The Common Meal wishes to free people from the thumb or aristocratic oppression, or so they say. Their goals are to generally destabilize the infrastructure of the realm. They are hardly the most popular sort. Their aims frequently bring them into conflict with the Fiona as well as the Kith Roi.
Those were the major factions. Characters spent their time getting played by all sides and trying to decide what is right to do.