I second the Reston Town Ctr peds. It's right outside of Herndon...
My son went there from birth to 5yo, but they dropped my insurance, so we had to leave... I'd go back in a heartbeat though! We would see any Dr there--I liked them all.
I've interviewed several peds offices since, and here are some things to note about Reston Town Ctr Peds:
~They have separate rooms for "sick" & "well" kids. Not just a different area (because we know germs know better than to cross that invisible line of separation

).
~Their on-call service is GREAT. There is a fee ($15, maybe?), but when a child is really sick, it's worth talking to a live nurse. They're also willing to fill a Rx during a weekend/holiday for something common like pink eye, and other places weren't willing to do that for us.)
~There are enough Dr's there that I've never had a problem getting an appointment.
~They do almost ALL blood work in house, and if not, the hospital is right across the street. *An odd note, perhaps, but I ran into that at a few other offices... I was expected to go to a lab for all blood work! With kids, this is a ridiculous expectation!
HTH