Dr. Phibes is my favorite of his roles. I got to interview him back in my college days for the school paper. It was surreal sitting at a table with him.
Thought of another one. Brad Dourif. He's excellent every time he plays a bad guy, creepy guy, eccentric guy, or just a crazy doll (LOL.) Original Dune movie, The Chucky movies, The Lord Of The Rings: The Two Towers, Alien Resurrection, and many more, including TV roles. Just look at all his roles in his filmography. Many of them, especially early in his career, he was a creepy/crazy bad guy.
I think the Xenomorph was unfairly type-cast as a "bad guy". Maybe someone will cast it as the lead in a romantic comedy, and we'll see it's range as an actor.
I haven't seen it in some time but i remember Laura Linney, in Mystic River as being absolutely frightening.