Crab Cakes in DC or Alexandria
If you do a search you'll find a ton of responses on this topic. Oceanaire and DC Coast often have very highly rated crab cakes (I love Oceanaires). CF folks during weekday lunch for a little bit cheaper.
DC Coast Restaurant
1401 K Street, NW, Washington, DC 20005
I still would rec CF Folks in general but their crab cake isn't what it used to be. 12-18 months ago the old chef left. I went nearly a year ago for a crab cake and while they still served it, it was off the menu (they were actually overjoyed somebody ordered one). It was not good, and I used to call theirs among the best in DC.
I have, however, gone a couple of times since and ordered specials, and have never been let down on that front.