The scene with the young Dastan protecting Bis from the guard who tried to beat him within an inch of his life.
Dastan faces Tus (who is convinced that Dastan conspires to take the throne) and explains the power of the Dagger of Time, then kills himself with it, trusting that Tus will believe him and use the Dagger to undo his death. He does.
Watching Dastan and his brothers together again after Dastan unknowingly hit the Reset Button and everything has been changed for the better.
In the end Dastan and Tamina are again shoehorned into an Arranged Marriage, only this time both are a bit more respective to the idea.
The best part? Tus is the one who suggests it this time around instead of their father.
Garsiv actually shoves Dastan into the arrangement.
Garsiv: Get up there, before I take your place.
Dastan's reaction to the proposal this time around.
Dastan: It's customary when proposing to present a gift, but I was caught off guard. I have nothing for you, save (pulls out the Dagger and presents it to a shocked Tamina) that which is already yours.