Internal Revenue Service lists all the charities that are registered as a 501(c)3, which is a requirement if you plan on listing your donation as a tax deduction.
The Better Business Bureau has an extensive and trusted database on charities.
Charity Navigator, one the largest evaluator of charities, has assembled a list of charities they recommend for Haiti, along with specific tips on donating to assist with the relief effort
Guidestar has one of the largest database on charities that includes extensive information on each organization's management structure and finances.
The Center for High Impact Philanthropy at the University of Pennsylvania has a blog maintained by disaster relief experts full of tips on how to make sure your donations have the desired effect. (http://blog.impact.upenn.edu/)