One from the pilot towards the end of the "Dancing on Air" song. Megan has spent most of the flight doubting that she could be of any help despite Firefly's assurances. But Firefly doesn't give up on her, and after she tries one more time Megan is at last convinced. Her voice fills with hope and delight as she joins Firefly in the final repeat of the chorus.
Twilight comforting Ember and telling her she'll grow up to her own special pony. Admit it, its adorable.