I used to sing this one to my daughter at bedtime and she loved it. Then as she got a little older and more defiant like her mother, I would tease her saying as she was halfway up the stairs to her bedroom, that the sandman was at the top of the stairs. She'd come bolting back down those stairs screaming and my wife would get pissed at me.
http://www.youtube.com/watch?v=Zbbuv5knJ4o