Give a shot on apartments near the Pentagon City metro. They are within walking distance from the metro. Just 2 stops from DCA.
I'm biased against Alexandria because of the longer walking distance and that a supermarket is not within walking distance. Disclaimer: I live in Arlington.
If you want to go a little cheaper on the rent, check out Columbia Pike. Try Archstone Apartments. Or you can rent someone's condo in the Brittany Condominium or Barkley Condominium. Disclaimer: I live in the Brittany Condominium.

(Sorry, I have nothing to rent at this point.)
An up and coming area is Shirlington.