This Nation
This nation.com: u.s. Supreme Court: Buckley v. Valeo, 424 u.s. 1 (1976)
This appeal filed in the U.S. Supreme Court describes the expressed powers of Congress to oversee the elections of President, Vice-President and Congress.
University of Groningen
American History: Outlines: The Reach of Congress
Although short, this article very clearly describes the investigative powers of Congress and their importance. Links to other American History topics are available, as well.