Paranormal Activity.
Hardly anyone I know has seen it. It’s not slasher horror, but it’s not a too-terrible psychological thriller.
Paranormal activity was actually good IMHO. Wel, good as in having your GF crush you instead of snuggling due to her being afraid hehe.
The ending of the late 90’s film Haunted with a young, naked kate beckinsale I also recommended. Well, not because she’s naked which is a plus, but the ending blew everyone away...and rumored to be the ending that M Night Shyamalan stole for the 6th Sense.
How about Exorcism of Emily Rose?