One of my favorites is the "The Phillips Collection" which owns a huge assemblage of modern art (phillipscollection). The place isn´t part of the popular museum row but you can easily reach the location in DC´s popular Dupont Circle neighborhood by subway (Red Line of the Washington Metro).
The museum was founded by the industrialist Duncan Phillips and Marjorie Acker Phillips in 1921 who - according to Wikipedia - believed strongly in the continuum of artists influencing their successors through the centuries (wikipedia). According to their website you can find there more than 3,000 works, ranging from masterpieces of French impressionism and American modernism to contemporary art.
I fell in love with the painting "Luncheon of the Boating Party" by the French impressionist Pierre-Auguste Renoir. According to Wikipedia the picture shows friends of Renoir who often were invited to his boat parties (wikipedia).The image, which is full of light, catches the party atmosphere perfectly. The displayed persons seem to live and you almost can participate in their joys. And Renoir is telling stories. On the right side a young woman is flirting with 2 men who seem not to mind competing with each another. The corner above on the right side shows another supposed ménage à trois. Others are contemplating or just enjoying the drinks.
And there is much more to discover, including paintings by Vincent van Gogh, Henri Matisse, Amedeo Modigliani, Claude Monet, Pablo Picasso. The famous Degas`s "Dancers at the Barre" got my special attention and the Hoppers too.
Here are some tidbits. Enjoy!