The very end, The screen will say "Ten years later"
Then you see Elizabeth and a kid walking towards the cliff and the kid is singing "Yo ho yo ho a pirates life for me".
Showing the crowd that this kid is Will Turners son. You see a green flash when the sun sets, and Will Turner hanging off the side of the mast because he is finished 10 years of the Dutchman and Elizabeth DID NOT betray him.
One VITAL piece of information has been lacking from all the answers thus far....
The little boy who is walking with Kiera, awaiting the return of Will...
IS THE SAME BOY THAT WAS HUNG AT THE BEGINNING OF THE MOVIE!
Remember that little boy that had to stand on the barrel in order to get hung. It's the same kid.
Don't know what the meaning is, etc., but that's what makes the scene so spectacular.