A good farmer's market is the Reston one, at Lake Anne. You'll also be able to see a bit of "historic" Reston. It's on Saturdays. There should be some closer, and I'd imagine there's one in Leesburg, but I'm not sure where or when.
From your other post, you've moved from Texas. I was going to say Mighty Midget in Leesburg, but you might pull BBQ rank on me. For a nice meal, Lightfoot in Lburg is a good bet.
Also there are a good few taco joints all over - most are run by Salvadorans, so they have a taste that's not LA or SF or Tex Mex, but still good. http://www.chowhound.com/topics/show/... is a recent post covering many, including my list of Reston/Herndon - note that two are in Lake Anne.
You should also check out Sweetwater on Rt 7. It's a small local chain (Great American Restaurants -> google it) where they do a slightly different take for each type of resto.
There are some posts for Loudon county, including one sort of recently, and quite a few on Reston and Herndon.
As you find things, post back your findings and further questions. It's such a wide open request that it's hard not to write a novel back to you.