Primary sources are original records created at the time historical events occurred or well after events in the form of memoirs and oral histories. Documents produced by government agencies such as Congress or the Office of the President and annual reports from agencies are also primary sources.

Great Primary Sources include:

Debates of Congress X1.1 and the HineOnline U.S. Congressional Documents database
Annals of Congress 1789-1824
Register of Debates 1824-1837
Congressional Globe 1833-1873
The Congressional Record1873-present

Congressional committee documents and reports, including agency annnual reports Y 1.1/2: and Readex U.S. Serial Set Database
American State Papers 1789-1838
The United States Serial Set 1817-present

Congressional Hearings- Testimony and transcripts on a huge varity of topics. Hearings are in the Y4 section, use the library catalog to find the committee you need.

The Library of Congress has many Primary Source Sets.

American Memory: Historical Collections for the National Digital Library

The American Revolution and The New Nation, 1763-1815

Use our cataloge to find the many secondary sources in the collection like these:

Intelligence in the War of Independence - U.S. Central Intelligence Agency
Call Number: PREX 3.2:IN 2 microfiche

List of Black servicemen compiled from the War Department collection of Revolutionary War records - Debra L. Newman, comp.
Call Number: AE1.115:36 microfiche

March to victory : Washington, Rochambeau, and the Yorktown Campaign of 1781 - Robert Selig
Call Number: D 114.2:W 27

A history of Indian policy -Tyler, S. Lyman
Call Number: I 20.2:H62

25 Years of the Safe Drinking Water Act: History and Trends, December 1999
Call Number: EP 2.2:D83/8

Women who made history a guide to women's history sites in Washington, D.C. - President's Commission on the Celebration of Women in American History.
Call Number: PR 42.8:W 84/3/2003012596

Many secondary sources are available online:

Many government agencies have departments that chronicle the history of the agency. The department of defense has many publications on the history of WWI, WWII, Vietnam, the Army, Navy, and military divisions including surgeons. The U.S. National Park Service and the U.S. Forest Service have histories of parks and wild areas.

Some other agencies that will have historic information are:
Health and Human Services
Smithsonian
U.S. Department of Agriculture
Interior Department
Department  of State