Try this link: http://www.washingtonpost.com/real-estate/dc-apartments-rentals.html?hpid=bottomnav
It will take you to The Washington Post rental page. Here is the form you will see. I have select "roommates" from the drop down menu for Categories, and entered "metro" for Keywords. Then I selected VA since that is where you say you wanted to look.
If you want to specify locations in VA, try Alexandria, Arlington, and, lastly, Fairfax. Alex. and Arl. are near DC....Fairfax County can stretch for many miles to the west from DC.
Here is the link to the Metro system map so you can see the name of subway stations. Virginia has blue, yellow and orange lines. It is in the lower left of the map. ... http://www.wmata.com/rail/maps/map.cfm