Federal Regulatory Agency List: This list, on the Federal Register website, includes agency information and links to agency websites.
United States Government Manual: "As the official handbook of the Federal Government, the United States Government Manual provides comprehensive information on the agencies of the legislative, judicial, and executive branches. It also includes information on quasi-official agencies; international organizations in which the United States participates; and boards, commissions, and committees."
Federal Administrative Agencies Guide (Pace Law Library)
Sourcebook of United States Executive Agencies (Vanderbilt University)
Describes the agencies of the federal executive establishment, their diverse characteristics, their place in the executive, and how their features influence political control and performance. It describes the evolution of the federal executive and notes emerging trends.