Matchbox is one of my favorite restaurants in DC, and the Capitol Hill location is great. Also, Busboys & Poets is great. I've only been to the Shirlington one, but I know that there's one downtown at 14&V too. If you've got a group of people, Buca di Beppos can be a lot of fun. Another vote for Julia's Empanadas as well.
Let us know where you end up trying, and what you think!