Accounting and Financial Reporting Guidance from the U.S. Securities and Exchange Commission, includes Staff Accounting Bulletins
Central Accounting Reporting System (formerly: Governmentwide Accounting and Reporting Modernization, U.S. Department of the Treasury)
FinCEN (Financial Crimes Enforcement Network)
Government Accountability Office (GAO) formerly the General Accounting Office
Internal Revenue Service: Official site with the Internal Revenue Code, forms, publications, regulations and information for tax professionals.
The Joint Committee on Taxation is a nonpartisan committee of the United States Congress, with an experienced professional staff of economists, attorneys, and accountants, that assists Members of both houses of Congress on tax legislation.
U.S. Chief Financial Officers Council (CFOC)
United States Tax Court: Tax Court and Memorandum Opinions from September 1995.
EDGAR Filings with the Securities and Exchange Commission (!0-K, 10-Q, 8-K, and so on) may be found at sec.gov.