Not really. DC just doesn't have that thrift culture other large cities do.

I've heard the Unique in Merrifield by the Mosaic District is quite nice, although it's a PITA to get to without a car so I've never been and can't personally vouch for it. The Unique in Silver Spring is also apparently good, but again, somewhat hard to get to without a car, although easier than the one in Merrifield...I think there is a bus from both Silver Spring and Ft Totten.

A couple of weeks ago I took the train up to Baltimore and went thrifting there. I was blown away by the selection and the number of shops...especially in the Hampden neighborhood. Worth checking out and makes a good day trip on the weekend.