From Strange Maps: Single Guys Live in LA, Single Girls in NYC. This is a map from National Geographic showing metropolitan areas in the US by whether they have more single men or single women. The LA area has the largest plurality of single men -- the number of single men minus the number of single women -- and the New York area has the largest plurality of single women.
I think it might make more sense to show this in terms of percentages, not absolute numbers of people. (If I had their data and the time, I'd do it. I think the data is available from the Census Bureau.)
There is a similar map showing the sex ratio in each county of the US, which shows some of the same trends. The Northeast doesn't look like as much of an outlier on that map, though, probably because the Northeast has some very large urban areas. New York, Washington, Philadelphia, and Boston are #1, 4, 6, 7 respectively. But this isn't exactly what I'm looking for, because it counts children and married people. (Married couples almost always bring the sex ratio back towards 1:1, since except in Massachusetts they consist of one male and one female.)
I wouldn't be surprised to learn that states with more males have faster-growing economies, because places where the economy is growing faster probably have more risky ventures going on and risk tends to attract males more than females. The two cities out of the largest ten that have the largest proportion of females are Philadelphia and Detroit, which seems to support my idea.
Strange Maps also features a lot of other strange maps: the U.S. divided into a dozen or so smaller nations and the Antipodes Map, which visually illustrates that for most points on land, the point on the other side of the earth is in the sea. If you drill straight through the center of the Earth, you won't come out in China. Unless you're from Chile or Argentina, that is -- which are both countries from which I've had exactly one page view.