I\'m a fan of most Halloween, Nightmare, and Jason movies, but each lost its appeal in recent years, with the exception of H20 which was an underated sequel. However non of them were particularly scary.
My favs would include...
The Ring
Cabin Fever
Texas Chainsaw Massacre
and a new one Gothika
Also, a completely underated horror flick known as Jacob\'s Ladder also tops my list because it gets in your head and involves a lot of thought. Similar to the book Slaughterhouse-V.