John Locke, Second Treatise of Government (1690).Available free on-line
Samuel Eliot Morison, ed. Sources & Documents Illustrating the AmericanRevolution and the Formation of the Federal Constitution: 1764-1788 (1923).An excellent compilation of founding documents, state constitutions,pamphlets, etc.
Peter Oliver, Origin and Progress of the American Rebellion (1781).A Loyalist account of the Revolution, before the Treaty of Paris hadformally concluded it.
Adam Smith, An Inquiry into the Nature and Causes of the Wealth of Nations (1776).The founding tract of modern economics.