This is stolen from Lenny at http://dcartnews.blogspot.com/ my apologies in advance.
DC area art galleries are generally now centered on six loosely gathered gallery concentrations: Dupont Circle, Bethesda, 14th Street area, Georgetown, 7th Street corridor, and Old Town Alexandria.
First Fridays: With 21 member galleries and art venues, the Dupont Circle galleries has the largest number of galleries roughly concentrated around the Dupont Circle area of DC. Many of these galleries host openings and extended hours (generally 6-8PM) on the First Friday of each month.
Second Thursdays: Seven galleries in and around King Street in Old Town Alexandria host openings and extended hours on the Second Thursday of each month. Other galleries in the area, as well as the 83 artists studios inside the Torpedo Factory host different openings ad hoc.
Second Fridays: With 12 member galleries and art venues, the Bethesda Art Walk also has a good number of participating visual art spaces offering openings and extended hours (6-9PM) as well as a free guided tour on the Second Friday of each month.
Third Thursdays: A handful of art galleries and venues are within walking distance of each other around the 7th Street, NW corridor and still host (I think) joint 3rd Thursday extended hours and openings.
Third Fridays: The five galleries inside the Canal Square (31st and M Street, NW in Georgetown) host joint openings or extended hours from 6-9PM each and every 3rd Friday of the month. The other half dozen or so Georgetown galleries within walking distance host their openings ad hoc.
14th Street: Initially anchored by Fusebox Gallery, a handful of very good art galleries and art venues now congregate around the 14th Street, NW area and host openings at various times throughout the month.