National Constitution Center
I just got back from touring the National Constitution Center in Philadelphia and found it quite an enjoyable experience. The place is BEAUTIFULLY designed, with a very interesting layout and lots of multimedia presentations, touchscreen interactive exhibits, as well as fascinating artifacts from many different eras in the history of the nation.
I only made it up to 1950 before they kicked me out, about 20 minutes after closing. I guess I'll have to go back when I get a chance.
There were beautiful scale models of the Capitol (including, of course, the Senate and House chambers), the Supreme Court, and the White House. The models were excruciatingly detailed, and the Capitol building was about ten feet wide and five feet tall.
There was a 20 minute film at the beginning that I haven't seen yet because I wanted to try to see all the exhibits before they closed, so that's another thing to look at when I go back.
There was an original newspaper that published, for the first time, the text of the Constitution. This was on display behind glass and was really cool to see. The entire Constitution with all amendments was engraved in large glass or perspex panels hanging from the ceiling at an angle so that the words appeared to be just glowing and hanging in the air.
Thoroughly recommended if you visit Philadelphia. Don't miss the USS New Jersey, USS Olympia, USS Becuna, Franklin Museum, Independence Hall, and the Liberty Bell, either.