The Metropolitan Museum of Art in New York City is currently showing "Depth of Field: Modern Photography at the Metropolitan" and "Impressed by Light: British Photographs from Paper Negatives, 1840-1860".
They are both worth seeing. The "Impressed by Light..." is a very large exhibit and I found myself rushing through it as it was close to closing time. I intend to go back to have a another look at it. The museum will be install a new photo exhibit (from its permanent collection) every six months in its newly dedicated Modern Photography Hall.