President Barack Obama appeared in a video message from a plant in Indiana to praise volunteers, first responders and local, state and federal officials for their efforts after the deadly tornadoes.
He encouraged Americans to support one another.
Lady Antebellum performed a medley of songs. Nicole Kidman, Shania Twain, Courtney Cox and others appeared in video messages, telling stories of survivors.
More than 300 people were killed across seven states two weeks ago, more than 200 in Alabama alone, when a record number of twisters struck.