Rebecca DeMornay in Hand That Rocks The Cradle
"Grandmother" in Flowers in the Attic (even if it butchered the book)
Audrey II in Little Shop Of Horrors
Minnie and Roman Castevet in Rosemary's Baby
Joan Crawford in Queen Bee
Evelyn (Jessica Walter) in Play Misty For Me
and yes, Faye as Joan in Mommie Dearest (...even though the real villain in that situation was Christina
)