We have hosted three parties at Kellari Taverna in DC - - a dinner for 20 or so. I would highly recommend this restaurant, as it has some great preset menus, offering guests three or four main course choices. The restaurant is very flexible and helpful and the food always delights our guests. Great appetizers include spinakopita, filet mignon on crostini, and lemon grilled shrimp. The lamb chops are to die for. And the other appetizers, including eggplant/zuchini chips, are addicitive.
We have also eaten at the restaurant as solo diners and the food is always great. Try the lamb salad at lunch! Kellari is known for their fresh seafood as well.