This gateway leads to numerous public policy
research organizations and journals.
Most have a "liberal" or "progressive" slant.
On the other hand, lots of published and unpublished articles and papers
are available. I would think this site would be an excellent place to
look for research materials.
This is the famous Green Book.
It contains a wealth of information
(data, laws, analyses) pertinent to programs that fall
within the jurisdiction
of the House Ways and Means Committee.