Who would have thought to explore the Library of Congress for historical documents? Right now, I'm looking at George Washington's copy of the U.S. Constitution, complete with his own handwritten notes. Amazing to look at. Here is a page from the LOC site with quite a few documents available for viewing related to the Constitution. There are so many more topics to peruse I can hardly wrap my mind around what is available to view.
Love that site! Ben's Guide to the Government is another good one, especially with younger kids. I'm using the LOC one for a son's government class this next semester. MT3