Although I agree with most, I won't repeat what people have written about the great benefits movies can provide.
I would like to try to add some information and tips:
1. The movies you watch with students should be appropriate for the age level. I don't show movies with excessive sex, drugs, language, violence ect. to my high school students. (They can watch those on their own).
2. Decide whether the movie is a learning tool or just entertainment. If it's just entertainment, don't waste their time and money by doing a movie in class.
Many of the titles listed in this forum have so much slapstick comedy and visuals, that the students will tend to focus on that instead of trying to understand the dialogue and messages of the movie. A healthy combination of visuals/slapstick comedy and comprehensible dialogue is great.
3. Try to show movies that will give ESL students a better understanding of another culture. Right now I am working with students who will go to college in the U.S. so I pick movies that will show American culture, particularly high school/college life.
4. Pre-teach blocking vocab. Try to integrate it into your class in the days preceding the movie.
5. Have the students write a summary, or a description of their favorite character, so that they actually pay attention to the movie, not just the visuals, and reflect on the content of the movie in English.
6. Try to show movies they have not already seen. (I know someone has said this already). This may cancel out any movie made in the past ten years;) If they have already seen the dubbed version, they may not pay attention as much to the language, as they already know what is being said and what will happen. Also, they may be bored.
The language in older movies seems easier to understand than newer movies anyway. Thin 80's and 90's. This may just be my perception.
7. Get feedback after the movie. Did they like it? Why? Why not? What were their favorite parts? I also give them a few questions to answer during/after the movie.
8. Subtitles or no subtitles? I try not to use them if they are not absolutely necessary. The students tend to read more than listen if they are there, but I do want them to understand.
Here are a few movies I have done. Many are oldies but goodies. (They all reflect American culture/American holidays/high school life)
I have pre-teach vocab lists and questions I made for each of these movies, which I would be happy to share if anyone is interested.
Can't buy me love
10 things I hate about you
the goonies (they loved this)
Back to the future
Ernest scared stupid (for holloween)
trains planes and automobiles
Family vacation (for christmas)
don't tell mom the babysitter's dead
Encino man (i did a reading lesson on cave men the day before to prepare. This was a HUGE hit)
ferris buellers day off
bill and ted's excellent adventure
home alone (also a good christmas movie)