National Gallery of Art
Including pieces from antiquities to pop art, the National Gallery of Art is a world-class museum housing the private collections of philanthropists such as Andrew Mellon. The museum started out with a mere 126 paintings and 26 sculptures but today the collection numbers over 140,000 works - many dating back to Byzantium. This is one of the best values in DC - a worthy educational experience that you don't have to pay for. For absolutely no money you can see the current exhibits, listen to a concert in the library atrium, or stroll around the 6-acre sculpture garden - leaving you enough pocket change to buy a snack in the cafe or a souvenir in the gift shop.