Important State of the Union Addresses in History. The History News Network has this nice article on important State of the Union Addresses of past presidents. The featured include President Cleveland, President Monroe, President Wilson, President Truman, President Eisenhower, and President Clinton. It also provides links to related HNN content on the State of the Union Address.
From the Constitiution of the United States of America:
Article 2, Section 3 of the United States Constitution: "[the president] shall from time to time give to the Congress information of the State of the Union and recommend to their Consideration such Measures as he shall judge necessary and expedient."