HAL 9000 comes to mind. The lack of emotion is so creepy. Carry that over to other circuited characters, like WALL·E's Axiom co-pilot AUTO, and you have a classic scary computer (See also the Deus Ex Machina from Matrix: Revolutions and Vicki from Small Wonder).
Also, having to routinely put on Disney's Beauty and the Beast for my kids has helpd me appreciate the blend of animal vocals and pitch-shifting/sub-harmonics done with the Beast's dialog during his more brutish moments.
Oh, and the Mouth of Sauron from Return of the King. Awesome visuals aside, the voice and that grapefruit-squish sound when he smiles is great.