If you have a car, you can try Wonder Books in Gaithersburg. On the plus side, they’ll buy almost anything. On the minus side, you have to drive all the way out there, and they don’t pay very much. But really, who does? http://www.wonderbk.com/productcart/pc/viewContent.asp?idpage=2
Wherever you go, don’t get your hopes up. Best sellers will probably bring even less money than other books — demand is high, but supply is higher.