My favorites from home are:
Zero's- best subs anywhere. they started in Va Beach and have become a local virginia chain with one store way out west and one up north. The nearest one to me is 40 minutes away in Fredericksburg
El Rodeo- best mexican I've ever had
Franco's- Italian...yumm!
Baker's Crust- excellent gourmet sandwiches, salads, and desserts. Their Crepe Jamaica is the best. Rum-soaked bananas with coconut, chocolate, and whipped cream in a yummy crepe.
As for the metro area:
The Orleans House near the Rosslyn metro station isn't half bad for steak and buffet-type stuff.
Bullfeathers in Old Towne Alexandria is fabulous, too.
Cosi is definitely on the top of my list, too.