Yo dee, read the fairfax virginia post. I'd think if you're passing through your best bet is going to DC, Georgetown M-street (Foggy Bottom on the metro)... try Rhinos or other bars there. Or drive out to Adams Morgan. Try ballston, too, I really like it down there. Just take the metro to those places. From reston/herndon, I would find my way to 66 East, take it to Nutley St exit where the metro is and ride that in....
Virginia itself is kinda slow... I guess you could try Arlington... I spent my entire childhood 2-18 in Herndon/Oakton area and there is nothing there for adults. You can try Reston Town center during the day, or Tyson's Corner, but I'd still say your best bet would be DC. PM me if you got any questions or comments. Hope I helped you even though it was a little discombobulated. I just wrote what came to mind. I will be back in the area August 6-15. ~Zappa