We have a separate site listing sources of U.S. Presidential documents and more.
These are tools for finding Federal Government. See also the separate Watchdog Agencies page.
This is almost certainly the most comprehensive database of Congressional publications, some dating back as far as the late 1700's. Includes the complete texts of hearings and most other documents. An interesting sub-set of the database provides legislative histories. (Law Library subscription.)
These are tools for finding information from the U.S. Federal Government.
Federal Government Watchdog Agencies
Congressional Research Service, Congressional Budget Office, etc.
U.S. Congress -- Sites and Documents
Official publications, sites, and more.