Top 100 US Documents
Apparently there was a people's poll (guess I missed it!), but the list is pretty good and it is put together by the National Archives. It includes pretty much everything you'd want such as the Constitution, Declaration of Independence, Louisiana Purchase Treaty, as well as the Marshall Plan, Civil Rights Act of 1964, the Sherman Anti-Trust Act, Jefferson's secret message to Congress asking for funds for the Lewis and Clark Exhibition. Not only are all 100 documents in easy to read form, but the original is also shown (kind of nice to show the actual Gettysburg Address to your students). Most of the documents also have links that you can link to to get background, pictures, etc.