Trailers / Directory / Search / Rate / Importance

 http://en.wikipedia.org/wiki/Trailer_(film)

1. A "teaser" promotes an "up-comming" film (i.e. ...opening fall 2009). 
2. A "trailer" is usually for a completed film that has either a firm release date, or has already been released.
3. Both are meant to intice you to see the film.

http://teaser-trailer.com/

Spark
http://movieinternet.blogspot.com/search/label/Spark

Tube

1. https://www.youtube.com/user/movieclipsTRAILERS
2. https://www.youtube.com/user/FilmsActuTrailers
3. https://www.youtube.com/user/triviatrailers
4. https://www.youtube.com/user/BeyondTheTrailer
5. https://www.youtube.com/user/NewTrailersBuzz

importance
http://www.articlesbase.com/movies-articles/importance-of-film-trailers-for-both-film-makers-and-audiences-792854.html