One thing that DC is infamous for is brunch. I've never been to a city where brunch was such an event. Many restaurants offer a Sunday Brunch buffet that will satisfy anyone's appetite. Listed below are the restaurants I believe to be worthy of mentioning. I haven't been to them all.
Suggestions are always welcome.
1335 Wisconsin Ave. There's usually a pretty big line, but it's worth it. This is a great place for authentic Tex-Mex. There isn't one thing on the menu that is bad. Plus, if you like margarita's they make the best ever.