Jaleo is a three star Spanish Restaurant that features the best tapas in Washington, DC and was the winner of the 2006 Wine Spectator Award of Excellence. It is open fairly late, so it works great for a snack or dinner after a theater show. It also offers valet service, so you won't have to find a parking spot when you go. You can expect to pay for the great food and service though, so be sure to have a good amount of cash before you go.
There is no better place to go for Spanish food in Washington, DC, and they even have live music. With three locations in the Washington, DC area, there will be one within reasonable driving distance from your hotel.