Can't speak to being evil, as I just can't ever seem to make myself play out the game that way, but the benefits of being good are pretty sweet...
1. It's much easier to get the ladies when you're good. And let's face it, we all like getting the ladies. :wub: Well, unless you ARE a lady, in which case, it may not be such a big deal... but I digress...
2. It's easier to talk to / do business with traders when they're not so busy running away from your evil ***.
3. It's cool to have the townsfolk cheer you when you enter town instead of complaining about all the vile stuff you've done.
4. Bright armor looks cooler (it's all shiny and stuff)
5. You don't have to keep eating all those crunchy chicks to stay evil after doing good deeds like wiping all the bandit scum from the earth.
6. Same goes for slaughtering the undead, too...
I'm sure there are others, but that should get you started.