The National Science Foundation's Graduate Research Fellowship Program is open to graduate students in NSF-supported social science, science, technology, engineering, and mathematics disciplines who are pursuing research-based masters and doctoral degrees in the United States and abroad. This includes economics, psychology (non-clinical), anthropology (including cultural if quantitative enough), sociology, and political science if focusing on the "science" of policy making (usually this has some econ in it). The only significant restrictions are no clinical biomedical sciences (that is the divide with NIH) and no purely professional degrees (including MD-PhD programs).
Fellows share in the prestige and opportunities that become available when they are selected. Fellows benefit from a three-year annual stipend of $32,000 along with a $12,000 cost of education allowance for tuition and fees (paid to the institution), opportunities for international research and professional development, and the freedom to conduct their own research at any accredited U.S. institution of graduate education they choose.
For more information, please see the GSAS website.