The best and most accurate search engine for Northern Virginia is provided directly by the Metropolitan Regional Information Service (MRIS), which is the mid-Atlantic's Multiple Listing Service (MLS).  This MLS features listings from all agents in real time and is completely free to use.  Seach using location, price, house type, map or other options.  Use the layers on the maps to see school and county boundaries. Feel free to make an account to save listings and use their Mosaic system to share listings.  Even if a property is listed with another agent, Acquire can take you to see any available Virginia property.