An anime character who might almost fit the "arche-type", but is not actually a step-mother, would be Mikage Tsumura from Jubei-Chan. She bore a striking resemblance to Jiyu's mother, and her father fell for her momentarily even though he knew she was married. Of course, she was an enemy, but became Marafiki after being defeated. I forget how much she tried to assume the role of "mother" while plotting a way to steal the lovely eyepatch, but I think she was manipulative.
A non-anime example that can to mind was Sedusa from the Power Puff Girls. Image: link
In Saiyuki, Gojyo's stepmom hated him to the point were she tried to kill him with an axe. Gojyo was under her constant abuse and wrath because he was born a hanyou (half-demon, half-human) and that also means his father cheated on her (a pure demon) with human.
Sorry only could find the manga picture of the scene.