Here's a Washingtonian Magazine list of German cusine:
Cafe Berlin: German
322 Massachusetts Ave., NE
Capitol Hill
(202) 543-7656
Cafe Europa: French/German/Italian
7820 Norfolk Ave.
Bethesda
(301) 657-1607
Cafe Mozart's German Deli: Deli/German
1331 H. St., NW
Downtown
(202) 347-5732
Euro Bistro: Asian/Austrian/German/Italian/Thai
314 Elden St.
Herndon
Old Europe: German
2434 Wisconsin Ave., NW
Glover Park
(202) 333-7600
Wurzburg Haus: German
7236 Muncaster Mill Rd.
Rockville
(301) 330-0402
The only one I have personal experience with is Old Europe. Not cheap, but very good food.
Although it isn't German, I can also recommend Russia House in Herndon for Russian food. Also not cheap, but good.
Jack
Bavarian Chief just above Charlottesvilee on Rt. 29 is great.
Wurzburg Haus: German
7236 Muncaster Mill Rd.
Rockville
(301) 330-0402
I heard they closed.
When I was working in DC, I had lunch at Cafe Mozart's at least once a week. Great sausages! They get them somewhere up in Balt.