If you are on a budget, I would recommend the TourMobile. http://www.tourmobile.com/
It's $20/adult and $10/child. It's an all-day shuttle service that runs from Arlington Cemetary throughout DC. You can hop on at the Smitsonian, Arlington, and Union Station Metro stops. Go early. It gets crowded.
You can get shuttle van service to the DC hotels. To/From all downtown Washington, DC Hotels $ 22 - 1st person & $ 10 each additional http://www.supershuttle.com/htm/cities/dca.htm
The Washington Post has a nice guide for DC that is kept up-to-date:
http://www.washingtonpost.com/wp-srv/metro/usersguides/dc/MusHistSite.html
It's $20/adult and $10/child. It's an all-day shuttle service that runs from Arlington Cemetary throughout DC. You can hop on at the Smitsonian, Arlington, and Union Station Metro stops. Go early. It gets crowded.
You can get shuttle van service to the DC hotels. To/From all downtown Washington, DC Hotels $ 22 - 1st person & $ 10 each additional http://www.supershuttle.com/htm/cities/dca.htm
The Washington Post has a nice guide for DC that is kept up-to-date:
http://www.washingtonpost.com/wp-srv/metro/usersguides/dc/MusHistSite.html