I would try RED SAGE near metro center. They have private rooms as well as an upstairs which is more casual and a downstairs, more formal. Great food!

There is also Firefly in Dupont circle. They have a room which can fit your group if it is more towards the 30 side.

I live right near Red Ginger (can see it from my window) and have never been. My roommate has though and loves it.

In Georgetown, I truly believe that Neyla puts out great food and so does Paparazzi.

There is also Mee n Yu which has great private rooms.

I have heard great things about Blackie's House of Beef (it's nicer than it sounds) for groups too!

Hope this helps!