I travelled often from D.C. to Dream Wizards in the mid-1980s on the T4 and T6 buses, before I got my driver's license. There was Chimera Books too, just down the road, off Rockville Pike.
Still alive and kicking it seems. http://www.dreamwizards.com/
At some point in my tenure there, I traveled up to Baltimore to go to Avalon Hill with my boss. They had some sort of distribution center there, with a lot of miniatures, and I went to pick through their bins of random stuff and select the things that I thought would sell well. It's a great memory.
For any 40-something folks from the Washington DC suburbs out there, the store was Dream Wizards, in Rockville.