My favorite lullaby -- and, I think, the favorite of my boys as well -- is one which is best sung in a three-part round. The words are pretty basic, but the tune is absolutely haunting.

Russian Lullaby

Night time is falling
The moon will be rising
The stars will be shining
The sun's gone to sleep

Close your eyes
And I'll rock you gently
And wish you sweet
Dreams while you sleep

Good night
Good night
Now it is time to sleep
Good night
Good night
Now it is time to sleep