In my opinion the best Halloween film ever made (discuss) is John Carpenter's original Halloween. Although Rob Zombie's 're-imagining' was pretty visceral it doesn't come close to matching the sheer atmosphere and tension built up in the original 1979 movie.
Although some films lose their power to draw you in, this one never does for me and it's arguably Carpenter's finest hour. It's aged pretty well too and the score never fails to raise the hairs on the back of your neck.
Jamie Lee Curtis is great as the geeky small town teenage babysitter but my vote goes for the brilliant Donald Pleasance as Loomis the doctor who's not taken seriously until it's too late. He gets all the best lines of course:
"I spent eight years trying to reach him, and then another seven trying to keep him locked up because I realized what was living behind that boy's eyes was purely and simply...evil."