Congressional Research Services reports are prepared upon request from members of Congress and are intended for the use of members of congress. The CRS does not have its own Web presence, but its work is in the public domain.
An independent investigative agency that "works for Congress," charged with examining all matters relating to the receipt and disbursement of public funds.
Nonpartisan research agency provides assessments of economic impacts of programs, proposals, etc.
There are inspectors general who conduct audits, investigations, and inspections within about 60 Federal agencies.