"A think tank or policy institute, research institute, etc. is an organization that performs research and advocacy concerning topics such as social policy, political strategy, economics, military, technology, and culture. Most policy institutes are non-profit organizations, which some countries such as the United States and Canada provide with tax exempt status. Other think tanks are funded by governments, advocacy groups, or businesses, or derive revenue from consulting or research work related to their projects."
--Diane Stone 'Think Tanks and Policy Analysis', in Frank Fischer, Gerald J. Miller. & Mara S. Sidney (eds.) Handbook of Public Policy Analysis: Theory, Methods, and Politics, New York, Marcel Dekker Inc. 2006: 149–157.
While all sources have bias, it is important to find out about the think tank/institute and its agenda and funders, as this may impact the way that you consider and counter-balance this information.
As the only Washington, DC-based think tank that actively promotes bipartisanship, BPC works to address the key challenges facing the nation. They are currently focused on health, energy, national and homeland security, transportation, the economy, housing, immigration, and governance.
The Center for Strategic and International Studies (CSIS) is a bipartisan, nonprofit organization headquartered in Washington, D.C. The Center's 220 full-time staff and large network of affiliated scholars conduct research and analysis and develop policy initiatives that look to the future and anticipate change. (Their health focus is primarily on Global Health.)
The Brookings Institution is a nonprofit public policy organization based in Washington, D.C.. One of Washington's oldest think tanks, Brookings conducts research and education in the social sciences, primarily in economics, metropolitan policy, governance, foreign policy, and global economy and development. (Their health focus is primarily on Global Health.)