One of my favorite ideas that never quite went through was for a world I was designing with my brother via wiki. I don't think I ever settled on a name, but the basic idea was that alignments are tied to elements, and that the combination of alignments meant that people had a certain combination of elements. Humans, being basically neutral, had a healthy mix of each (unless they went through some extreme rituals), but extraplanar beasts had some serious differences.
In this scheme, I wanted to go with Fire for good, evoking the common images of cleanliness, purity, and warmth- I was heavily inspired by the Zoroastrian tradition (as explained by Wikipedia), wherein they would have simplistic rituals involving fire.
This leaves Evil with Water, naturally enough. What, life-giving water is given a bad rap? Yes, absolutely. And here's why.
With fire, you know what you're getting. It's clear-cut and simple. With water, its flat surface hides great depths, with foreign monsters in a bizarre world. It's dark down there, hostile to life itself. It's Lovecraftian, where the shores are mistrusted due to the fishmen coming up from the depths to hunt humans for food. Fishermen and sailors are the bravest folk of all.
In this scheme, the Elemental Plane of Water is a place of great evil, of treachery, and of demons. In this world, the Horror of the Deeps is a lord amongst demons, a king of the great fishy hordes.