Note: CRS Reports do not become public until a member of Congress releases the report.
The Congressional Research Service (CRS) researches public policy for the US Congress. It issues about 3,000 briefs, reports, short issue papers and longer position papers per year on topics under study by Congress; these papers are brief - under 50 pages. It is renowned for its non-partisanship and in-depth analysis.
Note: Sites have some but not all available reports, so check all to be complete.
Open CRS - report pages link to all available versions; include the wikileaks reports
CRS Reports - hosted by UNT Libraries collections all they find online back to 1990
FAS CRS - Reports - federation of American scientists
Congressional Research Service Reports - unofficial collection of CRS reports on national security-related topics.