National Geographic Magazine has an interesting page in this months magazine. It's a large map of the United States showing most major cities. Depending on the size and color of the dot that marks the city, it specifies if there are more single men then woman.
In large western urban areas there are definitely more single men than woman, while in the east there are more single females than males (with few exceptions). In a large number of cases there is 40,000 more singles of a particular gender living in these cities. In New York alone, there are 185,000 more single females (I sense a lot of single men thinking of moving somewhere ;-).
For more details, check out the map in this months (Feb, 2007) National Geographic Magazine.
5 Star Online Dating Sites
http://www.5staronlinedatingsites.com/article.php?story=Singles-Statistics-Nation-Geography