Dario Argento's Opera is another cool film by him. It came out in 1987 and stars Ian Charleson(from Chariots of Fire) and William McNamara.
The film is about a young opera star whose doing MacBeth and is stalked by a vicious killer. The best kill scene in it is when the killer ties the young girl up and puts needles under her eyes to make her watch him slaughter a guy who she just slept with.
If you have never seen this film before be sure to check it out soon. I have the 2 disc dvd version of it.