American Institute of Philanthropy (AIP)
Provides you with information about the organization, the charities they rate, and the method of grading charities.
http://www.charitywatch.org/

Charity Navigator
America's largest independent charity evaluator, provides free financial evaluations of America's charities.
http://www.charitynavigator.org/

GuideStar
Database of information about nonprofit organizations. Includes non-profit resources, user’s guide, classifieds and products.
http://www.guidestar.org/