The EITC is the largest poverty reduction program in the United States. Almost 21 million American families received more than $36 billion in refunds through the EITC in 2004. These EITC dollars had a significant impact on the lives and communities of the nation’s lowest paid working people, lifting more than 5 million of these families above the federal poverty line.

http://en.wikipedia.org/wiki/Earned_income_tax_credit#Impact

Organizations/campaigns:

• National Community Tax Coalition, an organization that supports the EITC and tries to help make sure people claim it
• Boston EITC Campaign