Haiti

"Any man's death diminishes me, because I am involved in mankind..."

For I was hungry and you gave me something to eat, I was thirsty and you gave me something to drink, I was a stranger and you invited me in, I needed clothes and you clothed me, I was sick and you looked after me, I was in prison and you came to visit me.' Then the righteous will answer him, 'Lord, when did we see you hungry and feed you, or thirsty and give you something to drink? When did we see you a stranger and invite you in, or needing clothes and clothe you? When did we see you sick or in prison and go to visit you?' The King will reply, 'I tell you the truth, whatever you did for one of the least of these brothers of mine, you did for me.'

Love ye therefore the stranger: for ye were strangers in the land of Egypt.

Red Cross

Yele Haiti

Mercy Corps

CARE

There are certainly other reputable relief agencies working in Haiti. These are simply ones with which I am familiar (Red Cross, Mercy Corps) or could find quickly.
Please feel free to recommend other worthy agencies in comments.