Congressional Research Service is the U.S. Congressional think tank which produces reports on any topic under consideration by Congress. These reports are:
There are a variety of institutions, organizations and websites that are publishing CRS Reports. Try the links listed below.
Full of useful charts and statistics.
Might be one particular aspect of a policy/law.
Makes a recommendation regarding the policy.
Congressional Budget Office (CBO) provides Congress with nonpartisan analysis for economic and budget decisions and with estimates required for the Congressional budget process.