The Legend of Madam White Snake is a famous one in chinese mythology. In fact, the story was adapted many times over and shown in various movie versions. The trailer for the upcoming movie to be released in September is on one of the main characters the monk 法海和尚 played by Jet Li.
I will not show the trailer here but one memorable movie adapted from this was Green Snake <青蛇> shown in 1993, and starring the famous Maggie Cheung as the titular character and the now retired Joey Wong as Madam White Snake. In fact, someone loves it so much that the music is still being played on his handphone.
Anyway, the moral of the story is good and evil is sometimes not so clear cut. I guess good is never always good and neither is bad always bad.