The Department of Treasury has an Office of Tax Policy. The Treasury Department produces General Explanations of the Administration's revenue proposals (known as the Green Books). Treasury also produces a number of reports relating to tax policy. The Department of Treasury would also be a good resource for statistical and economic information.
CBO's mandate is to provide the Congress with objective, nonpartisan and timely analyses to aid in economic and budgetary decisions on the wide array of programs covered by the federal budget and the information and estimates required for the Congressional budget process. One of the topics that the CBO reports on is Taxes.