This one seems pretty spiffy for downtown/core areas - http://www.downtownmap.com/dc/html/main2.html

As for the metro, the station neighborhood maps can be useful - go to the main website (www.wmata.com), click on the "metrorail" tab, stations, and then, under the particular station's page, there's a link to "Neighborhood street map from StationMasters Online." The system map should let you click on individual stations, to get there, too.