the saw movies are travesties, they are nothing more than low grade torture porn... If you think that's horror.. you're sadly mistaken. I commend the Mod for the poltergeist pick, but do yourself a favor and skip the Saw3 recommendation... ok... so lets talk horror

in no particular order:

Dawn of the Dead (1978)
Nightmare on elm street 1 and 3
Suspiria
High Tension

Dawn of the Dead/Shaun of the Dead (newer versions) are my favourite by far.

maybe not the best one
but for me ,it just SAW

The Exorcist and The Descent. And I actually liked The Descent more when the monsters weren't in it. Just my opinion.