I stumbled across Mom's Apple Pie shop in Herndon a few weeks ago and I thought it was worth a mention to you all. The place is kind of dive-y (more on this below) but the pies are excellent! It's located on Sunset Park Drive in a small shopping center just off the Fairfax Cty Parkway and Sunset Hills. They have a large range of fruit pies, pecan pie, cream pie, etc, and what I found very interesting is that they sell "outdated" pies at a sizable discount, so that instead of $9.95 you can get a few-days-old pie for only $5.95, and I could not discern any decrease in quality. (They also have frozen pies at an even lower price, though I have not tried these.)
The dinginess of the location may be explained by the place's imminent relocation to Sterling. The move is to take place in a few weeks, and is due to the owner of the building having sold the place and the new owner increasing the rent enormously. I am supposed to receive a mailing with the new location in a few weeks, and when I do I will post here, if anyone is interested.