If you happen to drive down to Richmond, VA, there is a great Modern design store...La Differance.
Their website is www.ladiff.com
Also, in Charlottesville, VA there is an EQ3 dealer/store...Under the Roof. Their website is www.undertheroof.com

Happy shopping!
jlwatson

Thanks for the tips, everyone. I wasn't able to make it everywhere, especially with so few businesses being open past 7 pm, but I did hit a number of these spots, as well as a couple nobody mentioned. Apartment Zero was definitely worth seeking out. I ordered a couple of Offi W magazine racks in birch there; they didn't have them in stock, but offered to ship them for free since they didn't, and their price wasn't bad. One place that wasn't mentioned that I liked quite a bit was Tabletop on 20th Street near Dupont Circle. They had a nice selection of lamps, and I'm kind of kicking myself for not picking up one of the mobiles they stocked.

My wife and I wandered over to the Clarendon section of Arlington one evening and stopped by Vesta Home. Very nice, bit beyond our reach at the moment, but some nice eye candy. Maybe someday. One of their daybeds would look very nice in our family room. There's another store a block or two away called Modern Classics Furniture that says they have over 1000 items in stock, but it turns out to be a little hole in the wall where you can look at catalogs. I'm not sure what that gains you over looking at stuff on the net.

I drove by Daniel Donnelly on Friday, and the window display had some interesting looking stuff, but there was never a time when I was available that they were open. Next trip.

We hit Good Eye on our way out of town Sunday afternoon. I liked it a lot. We wound up buying an early 60s Swedish teak floor lamp with original shade and a barkcloth pillow with a very atomic design. My wife is a sucker for barkcloth.

Millennium Decorative Arts and Contemporaria are going to have to wait for another time. Thanks for the tips!

Thanks for mentioning the National Building Museum! Just a quick correction -- the NBM is a private, independent institution, and not part of the Smithsonian. We currently have a great show called Liquid Stone: New Architecture in Concrete, featuring extraordinary recent work.