http://www.census.gov
The U.S. Census Bureau offers regular reports and the latest data on poverty in the United States.

http://www.ssc.wisc.edu/irp
The University of Wisconsin's Institute for Research on Poverty offers a wealth of information, including a newsletter with reports from their researchers.

http://jcpr.org
Site of the Joint Center for Poverty Research, offering working papers, newsletters, and links to other resources.