Go to the Internet Movie Database (IMDb) at imdb.com. If you can remember the name of a single actor or actress who was in the movie, type the name into the search box at the top of the page.
Select the actor’s name from among the search results, and view the list of movies he has been in under “Filmography.” The movies will be listed in reverse chronological order, with the most recent movies first. Scroll through the movies, keeping an eye out for a title that rings a bell.
If you can’t remember the names of any actors or actresses in the movie, search through the appropriate genre (romantic comedy, for example) at an online DVD store. This method will take longer than the IMDb search, but simply looking at the titles of similar movies might jog your memory.