When I visited DC, I was a bit overwhelmed by the sheer number of museums and galleries! A friend suggested the Hirschhorn for the Ai Wei Wei exhibit that was up during my visit. That visit was very cool – loved the amazing ceramic crabs and the social commentary underpinning all of his work. Highly recommend seeing his art if/when you can! The Hirschhorn also has several other exhibits. I really enjoyed the graphic, text-based work downstairs which I believe is a long term exhibition. The building is very modern and interesting in its own right and I spent a long time wandering through the outdoor sculpture garden.
Photos via Flickr user Will (infomofo), Clayton Shonkwiler, Tadd and Debbie Ottman, and Ken Mayer