If we are talking impromtu car shows, I know there is one at the Starbucks on Rockville Pike, Rockville, MD. Pete could give you a better idea of where it is. I don't know of any in northern VA.
FYI, because there is so much to do around DC cruising isn't nearly as big a deal as it is in the Mid-West. My Ex lived in Ohio and all they did was cruise Friday and Saturday night.
-Andy
