Fatal Attraction was a classic movie from 1987 starring Michael Douglas and Glenn Close as a married man and his mistress. Glenn Close played the 'other' woman (Alex Forrest) who quickly becomes obsessed with Michael Douglas' character (Dan Gallagher). After being unceremoniously rejected by Gallagher, Forrest turns crazy and tries to kill him and his wife.
A memorable scene is the last scene were they Gallagher and Forrest are in the bathroom. Gallagher basically chokes Forrest to death in the bath (so he thinks) but then she reemerges from the bathtub as a crazed knife weilding lunatic. Great scary movie