The good and evil worship of good and evil deities comes from my general distaste for alignment. There is a goddess of death in my campaign setting who rules over a hell-like plane where the souls of the evil dead reside. She is an evil deity who delights in the torment of the wicked. Under regular D&D conditions, her worshipers and clerics would be considered evil.
However, there are those who worship her as appeasement, hoping their sacrifices will stave off death. There are those who worship her as a deity of beginnings and endings, of death and rebirth, in a very reincarnationist kind of faith. There are also evil cults that worship her so as to bring about massive death and destruction, and there are individual worshipers who offer sacrifices at her temples in hopes that she will curse their enemies.
Riffing on this one of the big charms of Eberron, imo, is that it kept alignment (whereas most people just throw it out as their way of dealing with the issues it raises) but made it explicitly separate from allegiance / role. So you had a Lawful Evil vampire ruler of a land as one of the main people holding Eberron off from disaster, a Black Dragon could be a dangerous spy and assassin - fighting devils. Meanwhile a Gold Dragon could be your most fearsome opponent even whilst it behaved with honour, simply because its goals were opposed to your own. I like alignment (so long as you do the 4e "usually" preface to nearly all alignments), but I don't like this queer notion that it's some sort of a side in some cosmic battleground where an elf and a gold dragon automatically team up because they mystically share a team. I don't share an alignment with everyone I work with or am friends with in real life. I certainly don't feel obliged to date only within my alignment. So why should creatures in the setting do so? Separate alignment out from this weird interpretation of it as determining your role in the game and it becomes a lot more palatable to me. Sure those orcs are Chaotic Evil. But they're also the ones who patrol that pit-portal to the Abyss and destroy the demons that try to enter their world. Shake it up a little, imo.