It is freezing cold here in DC; you might be able to see that it's snowing outside. We spent the afternoon hanging around the Natural History and Air & Space museums. For me I think the latter is cooler.
If I can make a recommendation, the "How Flight Works" display, though it's a bit cheesy and sponsored by Boeing, is actually pretty interesting. Someone with a serious science background clearly designed and fact-checked the displays. They avoid a lot of the usual myths about flight and even dispel some of my pet peeves (the "equal transit time" explanation, for example). Good stuff.