The closest D20 product that springs to my mind is actually the
Iron Kingdoms campaign setting, where you basically have 6 gods who represent 6 spokes on a pretty simple wheel.
Menoth the (assumed) creator of everything. He brought order and law to the primitive humans, and his representatives protected them from the predators of the wild. His words are Law to his followers, and apart from being the "Old Faith" in the biggest kingdom of the area, there is a whole church state revolving around his worship, led by a LN high priest and a group of LE inquisitors and secret police.
The Devourer Wurm is the opposite, and Menoth's archnemesis. It represents chaos, destruction, the rule of strength of claw and fang. In his more benevolent aspects, it is the predators of the wild, the destructive powers of nature. It is the patron of wild shapeshifters and raging berserker tribes. Its cults are hunted by Menoth's church throughout the kingdoms.
Morrow and
Thamar represent Good and Evil on this wheel. Once siblings on a quest for immortality, for the freedom of thinking, creativity, and personal enlightenment, they split up over their opinions on how to utilize the abilities and powers gained. Morrow opted for an altruistic approach, encouraging his followers to develop their abilities to their fullest potential and help others with them. Thamar drove her followers to use their abilities for their own gain instead, without much respect or thought for the rest of society. Morrow's church is the most accepted, since it tolerates personal freedom a lot more than that of Menoth. Thamar fosters small cults and sects that work from the shadows to pick at the roots of her brother's church.
Dhunia represents "Mother Nature". She is the primary deity of the intelligent humanoids, like gobbers, ogrun and trollkin. The circle of life is their religion, and they worship her accordingly. Oppsing her thematically is
Cyriss, a pretty newly revealed goddess, who has dominion over mechanics, mathematics, astrology, and most other sciences. Since the Iron Kingdoms are pretty heavy on magical mechanika, this comes pretty much with the territory.
Creating a Law vs. Chaos conflict in that setting is as easy as having a group of characters be employed by the church of Menoth to exterminate a local cell of Devourer cultists as a starting point, and then letting that grow to whatever dimensions you like. As long as all characters are lawful, the church will accept them. Adherers of the faith would be more welcome, of course. But since most of the Faithful are busy preparing a war, resources are stretched thin, which is where adventurers can come in.
By the way, those deities are mostly human-centered, or for humanoids. Dwarves have their own pantheon of ancestors that don't split up along those lines, and so did the elves...until they managed to tap their gods on the Prime in their hubris, which led to the gods wander off after a few centuries to find a way back home, leaving most of their clerics powerless and mad.
![Devious :] :]](http://www.enworld.org/forum/images/smilies/devious.png)