flat share in DC? (Washington, D.C.)

Hi,
I'm hopefully moving to DC in August to start a course at American University (Van Ness/Tenleytown/upper red line kind of area)...
I was wondering how to go about flatsharing or lodging with a family, either somewhere around there, or (ideally) in Dupont Circle, Georgetown or Capitol Hill? Does anyone know of anyone looking? Or of good websites where you can find this kind of info?
Thanks!
Claire