Havana Breeze, 1401 K Street NW, Washington, DC, 202-789-1470, closed weekends, closes early, 5 p.m., Monday through Wednesday [Washingtonian | Yelp]
I resent them for their hours, but I have never been to a bad Cuban place in my lifetime. Except in Cuba, that is.
Update May 26, 2006: A commenter says this place is closed.
Update September 2006: Now the Lima Restaurant.
I think this place is closed. I work in the area and have been looking for it, but it is nowhere to be found.