Are Some Lies OK?

Does the ninth commandment "You shall not give false testimony against your neighbor" speak to the subject of lies? Is it always wrong to lie? When Pharaoh ordered the Hebrew midwives to kill all new born boys they refused. When Pharaoh asked why? They said the Hebrew women are more vigorous than the Egyptians and give birth before they get there. This of course begs the questions of why have mid wives in the first place if the babies come too soon. Then the Bible says that God blessed the mid wives and gave them children of their own. So it would seem that lying under certain circumstances is OK. What do you think?