Near Ft. Belvoir
You could always stop in at the Cosmopolitan, a Bosnian restaurant and bakery close to the Beltway (5902 N. Kings Hwy). I've never been, and I don't think I've ever read a report on Chowhound.
If you don't mind going out of your way to Rte 1, then the possibilities widen. Below is link to a report I wrote about Tacos y Tortas Guadalejara at 7862 Richmond Hwy.
Cosmopolitan is now primarily takeout. (They used to have table service, but moved into a smaller location.) Yummy...but not a "sit down" place.
Bar J (mentioned by a previous psoter) is long gone. There is a Tubby's Chili in either the same or nearby location. (Can't exactly remember where Bar J was.)
There was a glowing review in the Post this morning of the Fireside Grill in Lorton, not far from Ft. Belvoir: http://www.washingtonpost.com/wp-dyn/...
Landsdowne Center (the plaza w/ Red Hot & Blue) also has sit-down options for Japanese, Pho, Indian, and Thai, plus a Greek diner. None are great, but most are pretty good; I think the Pho place is the worst of the lot (but still not bad), and some of the creamier curries (e.g. chicken korma, butter chicken) at Samrat are actually very good if you're into that style of food.
Red Hot & Blue
6482 Landsdowne Center, Alexandria, VA 22315
6408 Landsdowne Ctr, Alexandria, VA 22315
Olympians Family Restaurant
6432 Landsdowne Ctr, Alexandria, VA 22315
Samrat Indian Cuisine
6480 Landsdowne Ctr, Alexandria, VA 22315
Rice & Spice Thai Cuisine
6466 Landsdowne Ctr, Alexandria, VA 22315
6406 Landsdowne Center, Alexandria, VA 22315