Partners in Health has been working in Haiti for 25 years. They may be the largest heathcare provider still operating in Haiti. My understanding is their infrastructure was relatively undamaged, although of course there is a lot that is unknown. If any organization in Haiti is in a position to help the people of Haiti, it's PIH.
Tracy Kidder's book Mountains Beyond Mountains featured this organization and it's director Dr. Paul Farmer. I gave PIH money that this month's budget doesn't really have, because next month there won't be as many people in Haiti to help.