Ben's Chili Bowl is worth a separate trip to U Street - one of DC's greatest food landmarks. You won't find burgers or hot dogs on the menu without a heaping helping of their signature chili on top. The chili is smooth and thick with just enough kick in it, the patties and dogs are top notch, and a milkshake is an ideal companion. The place is packed solid at peak hours, but the staff have got the operation running like clockwork, plowing right through the lines while managing to be gracious and chatting up long-time regulars (of which there are quite a few). (Not getting yelled at - much as I love my NYC lifestyle - was my first sign I wasn't in the Big Apple.) The operation is all black-owned and operated, and got a visit from President Obama himself, a fact proudly telegraphed all over the store.
If your date decides he/she can't handle the grease, Ben's has also opened a more formal place "Next Door", minus the chili, but I haven't been able to resist the Chili Bowl to find out how it is.