Below is a partial list of 'think tanks' and policy centers that may be of use to you.
For focusing on domestic issues:
The Brookings Institute - http://www.brookings.edu/
The Cato Institute - http://www.cato.org/
The Heritage Foundation - http://www.heritage.org/
Center for American Progress - http://www.americanprogress.org/
American Enterprise Institute - http://aei.org/
For focusing on foreign policy:
Council on Foreign Relations - http://www.cfr.org/
Center for Strategic & International Studies - http://csis.org/
Wilson Center - http://www.wilsoncenter.org/
Wikipedia has an extensive list of think tanks. You may want to look through it.
http://en.wikipedia.org/wiki/List_of_think_tanks_in_the_United_States
High-quality journalist sources
The Atlantic - http://www.theatlantic.com/
The Economist - http://www.economist.com/
Foreign Affairs - http://www.foreignaffairs.com/
The Christian Science Monitor - http://www.csmonitor.com/
Don't forget that all of the Executive Departments (State, Treasury, etc) have their own studies and publications as well as all if the Congressional Committees (Foreign Affairs, Budget, etc).
Good luck.
