s1ty m said:The Exorcist. Desperately slow first hour, but then it goes really creepy and weird. The deleted scene of the spider walk down the stairs is appalling and should have been left in. I saw that cut scene on the Internet years after seeing the final version, really unpleasant. Cracking film.
The Ring is quite good.
I suspect Alien, the original, is more suspense rather than horror, but it has some great moments.