The GAO is a government agency that provides auditing, evaluation, and investigative services for the United States Congress. The are the "Watch Dog" of federal government. GAO reports are:
Full of useful charts and statistics.
Might be one particular aspect of a policy/law.
Makes a recommendation regarding the policy.
Search the GAO here:
Congressional Research Service is the U.S. Congressional think tank which produces reports on any topic under consideration by Congress. These reports are:
Hard to obtain. They are not made available to members of the public by CRS, except in certain circumstances.
Objective reports produced for committees in congress to analyze issues.
Widely regarded as in depth, accurate, objective, and timely.
Excellent resources for legislative or public policy research.
There are a variety of institutions, organizations and websites that are publishing CRS Reports. Try the links listed below.