The Congressional Research Service (CRS) is a division of the Library of Congress. They produce analytical, non-partisan reports on topics of interest to members of Congress. While they do not maintain a public website for dissemination of these reports, there are a number of free and subscription sites where you can find CRS reports. You can also request copies from your Congressional Representative.
Tax Specific CRS Reports are also available on:
University of Cincinnati Libraries
PO Box 210033 Cincinnati, Ohio 45221-0033