ringu (1998)

aka Ring.
Reiko is a divorced mother of one, and tv journalist, whose niece was recently found dead of shock. When she learns that three of her niece's friends have also died, she decides to investigate. She discovers they all watched a disturbing videotape, and that anyone who watches it dies seven days later. She recovers a copy of the tape but time becomes critical when first she, her ex and then her son accidentally watch it.
This masterpiece of Japanese suspence brought a new wave of Asian horror to western eyes. The film starts slowly, but inexorably builds to its climactic end. A must see, as simple as that.