Personal opinion after about 15 years living in the area.

Borders has large CD departments, at least in some but not all branches (the
one in Rockville MD is quite big, for instance) but the prices aren't great.
It is incomprehensible to me how they can continue this way with Olssons and
Tower at least from week to week offering some sort of special.

The Olssons in Georgetown (Wisconsin Avenue just above M Street) and
the Tower in Georgetown (20th and Pennsylvania) might well be the most
rewarding places to go.  [Usual disclaimer-my older daughter works at
Olssons on college vacations].

Tech Hi Fi, who sell used classic audio equipment, have sometimes
interesting used classical CDs; there's a branch in Bethesda on Old
Georgetown just off Wisconsin, and another somewhere in northern Virginia.

Self promotional addendum:

I'm conducting a choral concert Saturday night, 30 October:

Psalm settings by Bernstein, Nielsen, Sweelinck, Monteverdi and Brahms,
with a professional chamber chorus, the Woodley Ensemble, 8 PM at St.
Paul's Episcopal Church, Georgetown.

And a performance of Pierrot Lunaire in English [excellent Halloween fare!]
on Sunday October 31 at 3 PM at the National Institute of Health, Bethesda.

Schoenberg-haters, note: not the National Institute of Mental Health.

Feel free to email me if either is of interest.

Joel Lazar
Visit my orchestra's site at http://www.jccso.org/