Hopefully this New Moon trailer stays live for awhile, as the typical battle between copyright infringement and uploads is already going on, as Viacom tries to keep the video from being seen outside of their control.
Anyway, this one has been kept up for some time, so hopefully when you see it, it'll still be running.
The trailer itself shows the deepening love between Edward Cullen and Bella Swan, and the decision he makes to leave her in order to protect her.
Then it swings to after he's gone, and conflict with Bella and other unsavory characters.
The finale of the transformation into a werewolf is great, you've go to see that.
Vampires - New Moon Trailer