Dave- what's your budget, what kind of framing do you need to do, and what quantity of work are you looking to frame? There's lots of little mom-and-pop type frame shops in and around Arlington, most of which will do a competent job. If price is either a minor or a non-concern, then I can highly recommend Mickelson's in downtown DC. They do work for the National Gallery. I usually take stuff to them when I have something antique or unusual that needs special handling, like a 3 1/2 foot circa 1820 chinese silk Imperial Edict, or a pencil sketch on discolored paper from the 1910's that may be by Sargent. Mickelsons has been in business since the early part of the 20th century, so if you need an unusual frame for something, they're the best place to go as they still have vintage moldings in stock. They will also do things like use 8-ply mat board, which many frame shops refuse to do.
For someone less expensive, but who does high quality work, I can recommend Framesmith (just off 14th Street, in the Logan Circle neighborhood of DC). I raid their overstock frames bin every summer for my own stuff when they participate in the annual sidewalk sale that the 14th Street merchants organize. I want to say she's on Corcoran, just off 14th, but it could be on Q or the next street up from Q as well. Paula Amt is the woman's name who owns it, and she also owns Plan B gallery on 14th.