The 'teaser' that many of us have already seen is the end of the preview, where we get some short interview from Sean, Viggo, Eliah and PJ as well as a few other directors, Alan on Minas Tirith etc.

We get to see a lot other short clips from diffrent stages of the film. A few scenes of Frodo running in Shelob's cave. (awesome) The entrance to the Path of the Dead Sequence.

A scene between Merry and Pippin, where Pippin is informed that Sauron now believes that Pippin has the ring and thus is after him.

A scene with Denethor, who is not pleased about this "ranger of the north"

Several snap shots of Minas Tirith, and also a sequence about Massive, their program for making the armires move. (In which we get to see some flyby scenes from the battle).

There is a long sequence from Pelenor Fields, where we get to see lots of horses attacking, a cool scene (in Massive) where an Oliophant tries to stomp some horses. Merry charging (in full armor).