CityWalkingGuide.com and NationalGeographic.com offer good walking tour maps of Washington D.C., covering the National Mall, the White House, monuments, museums and galleries. The book "Washington on Foot," edited by John J. Protopappas and Alvin R. Mcneal, contains maps covering both lesser known and famous places of interest.
The City Walking Guide website offers seven different walking tour maps, which users can pay to download for printing out or for use on a mobile phone. The National Geographic website provides a free downloadable map covering key sites of interest. With 24 walking tour maps of Washington D.C., the book "Washington on Foot" is available for purchase on Amazon.com in both paperback and Kindle format.