The National Gallery of Art is so vast, you'd need at least 2 days to enjoy it in its entirety. I had 3 hours but I was there 3 years ago and got to view some great pieces then.

The two main pieces I wanted to see were the Capitoline Venus and the Declaration of Independence in stone (which I didn't get a photo of --I don't think we were allowed):

A few other pieces I really enjoyed:

The Temptation of Saint Anthony, Follower of Pieter Bruegel the Elder

The Fall of Phaeton, Sir Peter Paul Rubens

Ships in Distress off a Rocky Coast, Ludolf Backhuysen

The Shipwreck, Claude Joseph Vernet

Joshua Commanding the Sun to Stand Still upon Gibeon, John Martin

The Spirit of War, Jasper Francis Cropsey

Voyage of Life series, Thomas Cole:

Childhood

Youth

Manhood

Old Age

El Rio de Luz, Frederic Edwin Church