I've only shopped for gear at these places, but out in Leesburg there are two decent shops: Bicycle Outfitters and Plum Grove Cyclery. There's also Spokes, Etc, scattered throughout NoVa. I've been meaning to check out their shop in Ashburn, but haven't made it down there yet. Any place that shows a kid's Kettler Jumbo and a Trek Madone as featured items on their home page has to have a cool atmosphere.

If you haven't already, make sure you check out the Mid-Atlantic forum here at TE. There's a good number of us DC-area TE'ers!