As you know, Haiti has been hit by the biggest earthquake in 2 centuries and thousands are feared dead. The living have the immense task of rebuilding after the devastation. And many of us are thinking of ways to help. After the tsunami in 2004, millions of dollars were raised and sent to affected areas, only to be found to have been wasted. When Nargis hit Burma last year, many of my friends were asking, 'who do we support? How can we be sure donations aren't wasted, that they get to the people in need?' These are difficult questions to answer.
In times of emergency, aid is more likely than usual to be diverted away from the people who really need it. Food, medicines, supplies need to be distributed fast and this prevents necessary checks being put in place to ensure support is going to those who need it most. Haiti scores lowest in the annual Corruption Perception Index released each year by Transparency International. This will make it even harder to aid agencies to do their work on the ground without the risk of diversion by the powerful. It's an unfortunate reality.
This does not mean that we shouldn't give Haiti as much support as possible. It just means that you should do your research when giving. Give to organizations that are already established and have a history of operating transparently and effectively in-country. These organizations and their people on the ground have already built relationships and know their way around. They can quickly establish fair channels of distribution and get your donations to where they need to go most.
Personally, I would avoid giving to any UN agency. That's a personal bias, based on my experiences in Cambodia and from anecdotes from elsewhere. UN agencies are large, bureaucratic, slow and already very well funded. They don't need small donations. I'd try to find a locally founded and based organization that focuses on the country, is run by locals but with sustained outside support. One such organization in Haiti is the Restavek Foundation. They are already in place, working directly with schools that they have been working with for years, ready to get assistance to those in need. Go here to read more about their post-quake situation.
The other organization I would donate to in any emergency situation is Doctors Without Borders/Médecins Sans Frontières (MSF). If anyone knows how to get help to people in emergencies, it's them. They already have clinics set up in Haiti and like Restavek are able to distribute aid through already established channels.
From the early reports it looks like Haiti is going to need a lot of support, immediately and in the coming months. Give what you can, but give where it will help the most.