Don't know where to start? Try one of the following database portals. They allow researchers to search across multiple databases produced by the same publisher.
Digital collection of early American imprints, broadsides and ephemera. Based on the American Antiquarian Society's collections: Afro-Americana Imprints, 1535-1922; American Broadsides and Ephemera; Evans, 1639-1800; Shaw-Shoemaker, 1801-1819.
Digitized library of economic and business literature on topics like the Industrial Revolution, the development of modern capitalism, and the emergence of modern economics.
Rich source of material on Early America (1789-1838). Covers events such as the Lewis and Clark Expedition, Burr's Conspiracy, and Native American/European relations. See also U.S. Congressional Series Set (1817-1933) and Proquest Congressional.