Bon Appetite (a.k.a. "The Bone") at 21st and I St, just south of Pennsylvania Ave. Great burgers, subs etc.

If you are up near the Zoo, and are feeling a bit adventurous, walk south on Connecticut Ave, cross the Ellington/Calvert Street Bridge into Adams Morgan and hit one of the Ethiopian places in and around 18th St. I prefer either the Red Sea or Meskerem.