I'm going to reccomend the original original Ju-On.
For reference, the Ju-On series consists of five movies so far, as far as I remember:
Ju-On: The Curse (made-for-tv, extremely creepy low budget) Ju-On: THe Curse 2 (unknown)
Ju-On: The Grudge (creepy, absolutely worth a watch, remake of the original, better SFX and stuff, but something is lost)
Ju-On: The Grudge 2 (remake of Curse 2, no clue how good it is)
The Grudge (american remake, supposedly rather good, stars Sarah Michelle Gellar, same director as the original movies. Haven't seen)
I'm also going to namedrop a movie which I really, really, really want to see: The Woman in Black. If you manage to get your filthy hands on this movie, I order you to make me a copy. It's a british made-for-TV horror movie based upon the book and play by the same name. I know folks who have seen the play and been thouroughly scared, and the movie is rumoured to be in a league above the play again. To quote a review from IMDb:
The book is sinister. The play is scary.
The film is devastating.
It is hailed among those who have seen it as possibly the scariest movie ever, and because it's so hard to find, those who have tracked it down generally know their horror, so...