Quite an interesting survey…
1) The Declaration of Independece
2) The U.S. Constitution
3) The Bill of Rights
4) The Louisiana Purchase Treaty
5) The Emancipation Proclamation
6) The 19th Amendment to the Constitution
7) The 13th Amendment to the Constitution
8) The Gettysburg Address
9) The Civil Rights Act
10) The Social Security Act
(and the spelling mistake is on the history site, heh, ironic, eh?). Note that the top 3 were already defaulted to the The Declaration of Independence, the U.S. Constitution, and the Bill of Rights.
but quite fascinating to see the relative rankings, eh? Why would the Louisiana Purchase Treaty go on the top?