What are good lullabies to sing to little kids?

I babysit little babys alot. But every time they start crying i rock them back and forth to try to get them to sleep again and i can never remember good lullabies to sign them to sleep... i do have some what of a good voice. =] if you could leave the names of some and possibly the lyrics to them also.. i would be very very greatful. Thank you so very much.