You can also view trailers for free online. Some of my favorite sites that feature teaser clips include TrailerAddict and Movie-List.com. Many movie entertainment sites include trailers as part of their content -- JoBlo.com, DarkHorizons, and ComingSoon.net, to name just a few. Trailers can also be found on iTunes and YouTube.
There definitely is an art to making a great trailer. It needs to be exciting and make the viewer want to see the entire movie. It has to give enough information to let the audience know what the film is about, but not too much where important plot information gets spoiled. It has to showcase some of the movie's key scenes and performances without giving away all the best stuff.
Sometimes, a trailer can be even better than the crappy movie it is teasing. Other times, a bad trailer can destroy any chance a film has for success.
Those bite-size chunks of cinema are a perfect appetizer for any movie fan, making them hopefully want to see more.