When left to labor on their own, many women find themselves wanting to get on their hands and knees. This position can be really great for taking the pressure of the baby off a woman's back. It also makes use of gravity to help get the baby out. Put something soft like a blanket under your knees when using this position.
Benefits: Gravity, eases back pain, feels natural, great for stuck shoulders or a posterier (face up) baby. Drawbacks: Can be tiring to hold yourself up, harder for attendants to see birth.