The ending. As Didymus and Hoggle say to Sarah, through the mirror, "And remember, fair maiden, should you need us..." "Yes, should you need us, for any reason at all...". It's what True Companions is all about.
There's more; "I do need you..." "You do? Well, why didn't you say so!?" (Sarah turns around and sees Ludo, Hoggle, Didymus, Ambrosius, and several of the labyrinth's creatures, including two fireys and the wise old man. They start partying.)
Sarah giving Lancelot, her teddy bear, to Toby in the end. Remember, she was furious that her stepmother or her father took it from her room in the beginning. Now she's acting like a good sister and sharing her stuffed animals with her brother.