The Dark Knight teaser trailer

This teaser trailer works by giving very very little away about the movie and also as it is very short, but is highly effective. Besides the cuts for the company logos, the title and the coming soon, the trailer is made of one continuous shot. Even though it fades in and out of black, you can tell from the post-glow once the blue light has faded that the shot hasn't cut. It hints at the plot through the use of the quotes, said by Bruce Wayne/Batman, Alfred (his butler) and the Joker, done as voice overs.

Bruce Wayne: I knew the mob wouldn't go down without a fight[2]But this is different[.] they've crossed the line.
Alfred:You crossed the line first sir[.]You hammered them[.] and in their desperation they turned to a man they didn't fully understand[1]Some men aren't looking for anything logical[.]They can't be bought[.] bullied[.] reasoned[.] or negotiated with[.]Some men just want to watch the world burn.
Joker: Starting tonight[.]People will die[2]I'm a man of my word [2]*manic laughter*

The quotes (shown as a transcript here) tell us that the movie is centered around the mob, and that they turn to someone for help, introducing the antagonist for this film, the Joker, without even saying his name, through the use of his manic laugh and the joker card that flies toward the screen at the end.

The Batman emblem, which is that is instantly recognisable, is slowly shown as rays of bright blue light shine from behind it, contrasting with the otherwise pitch black screen. As the emblem is revealed it slowly disintegrates, symbolising that the Batman is not quite as powerful in this as he was in first movie (where emblem becomes bats, which are his symbol so this still keeps with the idea of power). The fact that from the Batman emblem comes a Joker card, symbolises that the lost of power is due to the Joker (who is introduced by a similar card at the end of the first movie, Batman Begins).

The mad laugh from the Joker, as it is clearly the laugh of a lunatic,is used specfically to make the audience uncomfortable even though we have no idea what the Joker actually looks like and what he does, nor do we actually know (unless we have previous information) who it actually comes from.