The original Dawn of the Dead. In my opinion it's about as close to the perfect horror movie as you can get.
That is how I feel about The Texas Chainsaw Massacre.
It just has EVERYTHING a great horror movie should AND it did not even need "gore" to scare the pants off people. There was no gore at all. They appealed to our imagination and the scary background noises/music just made it feel CREEPY during the whole movie!
Also, I just cannot think of any other actress MORE terrified and more REAL than Marilyn Burns! Man on man! All that screaming and going out of her mind at the end when she hops in a truck to freedom. She is laughing and crying at the same time and blood red from jumping out the window.
The whole "final" ending had such a SURREAL look to it!