US National Archives
Nara: The Marshall Plan
This National Archives and Records Administration site contains a brief definition of the Plan and has a picture of Marshall. There also are links to a couple pages of the Economic Cooperation Act.
OpenStax
Open Stax: Post War Prosperity and Cold War Fears 1945 1960: The Cold War
Examines the causes of the Cold War, America's efforts to oppose the spread of Communism, and the hunt for Communist sympathizers within the United States.
Harry S. Truman Library and Museum
Harry S. Truman Library: The Marshall Plan
This is a list of the actual documents with correspondence concerning the Marshall Plan.
Internet History Sourcebooks Project
Fordham University: Modern History Sourcebook: The Marshall Plan, 1947
This Fordham University site contains the speech delivered by General George Marshall at Harvard University on June 5, 1947.
Smithsonian Institution
National Portrait Gallery: George Marshall
This is a brief but informative piece on George C. Marshall - creator of the Marshall Plan. Includes pictures of most of the world players at the time. Describes his role in formulating the Marshall Plan.
Independence Hall Association
U.s. History: Containment and the Marshall Plan
Read about President Truman's two-pronged foreign policy for Europe. Find out about his containment policy and the Truman Doctrine, which was manifested in the Marshall Plan.
Other
Organization for Economic Co Operation and Development: Marshall Plan Speech
This resource provides the text of George C. Marshall's speech on the Marshall Plan as delivered at Harvard University on June 5th, 1947.