The Metro (or for you Anglophiles, "the Underground") takes you everywhere you want to go - most hotels are within a half-mile walk of a Metro station, and those that aren't usually offer a free shuttle to the nearest one.  For an overall layout of the Metro system, go to their website.  Stationmasters has a more detailed map of the system, including maps that show the surrounding attractions for the half-mile radius around each Metro station, including museums, art galleries, embassies, houses of religion, school and universities, and popular tourist sites. If you're planning to use Metro for the duration of your stay, I strongly recommend purchasing the guide, which is useful if you're looking for a hotel adjacent to a Metro station.

However, the Stationmasters map doesn't list the restaurants around each Metro station.  But fear not - TourofDC.org provides a dining guide of Metro stations and nearby restaurants, including links to restaurant reviews and directions.  Washingtonian Magazine publishes an annnual guide to the Best Bargain restaurants, and have topped that with an annual list of Cheap Eats for those who want to spend even less.  And for those on expense accounts, Washingtonian also publishes list of its 100 Very Best.  Note that many of these restaurants are Metro-accessible!