National Zoo
http://nationalzoo.si.edu/default.cfm
Jefferson Memorial - away from the Mall at the Tidal Basin
Einstein Monument - hidden away in a corner by the Mall, is a 3.5 times larger than life copper bas relief of Einstein with the stars mapped out on the ground. Very cool little nook, nice for a few minutes
Smithsonian’s Natural History Museum -
http://www.mnh.si.edu/
Camelot - Excellent high end strip club
Also the National Air and Space Museum, FBI, National Gallery of Art, National Geographic Society and Bureau of Engraving & Printing are in DC
If you have a car Annapolis is only 30 or so miles away as is Baltimore
Caution - DC is a very funky town to try to get around. Easy to get lost
Also some sections of DC I would not recommend
What kind of things do you enjoy? What would you like to see while there?