If you go to any search engine and type "Movie quotes search engine" into the search box you will get some of these web sites. There you can look for whatever you want, for instance, if you want to know in how many movies the word "Manhattan" is said or to know in which film the phrase "yes, we can" is said you can even have a look at the context.
These sites are also a great resource to make a video-montage (assembled from very short clips from several movies), using the time reference shown in the found results to cut the specific scenes to make the montage.
Another funny use of this type of web sites is as a tv-guide, if you turn on tv and a film has already started you can look for a phase you have just listened and you will know which movie is it from and how long has it been since it started.
Subzin is a new generation Movie Quote Search Engine with more than 15000 movies (>20 million phrases), if you are a real fan of movie quotes, you'll enjoy it.