I would highly recommend paying for the bus tour on one of the days or do the hop-on-hop-off bus that was discussed above so that you can get off and on and see whatever you want to see. It's a very efficient way to see the major aspects.

And then I guess the other questions are, are you a museum person, do you want to try to get tickets for the Holocaust Museum or to get into the Capitol building? I love personally to see the Constitution when I go. Ford's Theatre is another important place to see and many people enjoy the tours of the architectural neighborhoods and Georgetown. You really can't go wrong