Often referred to as Congress' think tank, CRS provides nonpartisan legal analysis to committees and members of the House and Senate. CRS is a legislative branch agency within the Library of Congress. CRS does not publish their reports, but some of the reports are available via the resources below.
Often called the "congressional watchdog," GAO investigates how the federal government spends taxpayer dollars. GAO issues reports on government programs and policies, and performs policy analyses.
The CBO provides nonpartisan analyses of budgetary and economic issues related to Congressional legislation.The CBO produces a variety of products, including analytic reports for particular federal spending programs, and cost estimates on all legislation.
Broadly stated, think tanks are non-profit organizations which perform public policy analysis and research.