The central tourist area is The Mall....the large grassy area that is ringed by museums, monuments, White House, and the Capitol Building.....if you watched Obama's inauguration, that's where all those people were standing. In this area are:
The Smithsonian Museums which has something for everybody...http://dc.about.com/cs/museums/a/Smithsonian.htm
The National Gallery of Art is not part of the Smithsonian but is in the same location in DC. ... http://www.nga.gov/
Of course, the monuments, White House, Capitol Building, Library of Congress, Supreme Court Building are all in the same area too.
Also there is the US National Archives if you want to see the The Constitution, the Bill of Rights, and the Declaration of Independencehttp://dc.about.com/cs/museums/a/NationalArchive.htm
Dupont Circle is the main gay area for bars etc ... http://dc.about.com/od/neigborhoodprofiles/p/DupontCircle.htm
The Phillips Collection is a small modern art museum just 3 blocks from Dupont Circle... well worth visiting ... http://www.phillipscollection.org/
My favorite bar in DC, however, is just 6 blocks east of the Capitol Building. It's called Remington's...a country western bar ... http://www.remingtonswdc.com/
Of course, there are the historical sites everywhere in DC and over in VA.
Probably most prominent in VA is Mount Vernon, George Washington's estate... http://www.mountvernon.org/
Hope that helps.....anything else you want to know?
Here is info on the DC metro....the best way to get around DChttp://dc.about.com/od/transportation/a/Metro.htm