We just went to the Olney Boys and Girls Club Field of Screams...
http://www.screams.org/...bit of a drive from NoVa but awesome and totally worth the price. Totally freaked me out.
Also I heard that Markoff set up a nearby attraction for Virginia-ers who don't want to drive all the way to Poolesville - it's at National Harbor
http://www.markoffshauntedharbor.com/index.html. Tickets are $15 which is cheaper than their Poolesville location but I'm not sure how good it's supposed to be...anyone been? But have to count in additional expenses like the ridiculous $10 garage parking if you can't nab a parking meter.