Actually, I was misinterpreting the news story I read, but there are two definitely within the neighborhood:

http://www.nytimes.com/2010/08/14/nyregion/14mosque.html

Both are overflowing and it was clear that there is a need amongst the Islamic communities for a mosque in that neighborhood.

There are also Islamic services every Friday in the Pentagon chapel. And, in fact, the chapel is in the part of the Pentagon that was hit - less than 100 feet away.