Dino is another good option. They will rent their entire upstairs to you, which holds 60. I had my wedding reception there and the food (we opted for family-style service) was awesome. Dean, the owner is flexible about menu options, and the whole staff will make sure you feel well taken care of. Most importantly, the food is good.
Info on group dining here (scroll down): http://www.dino-dc.com/private_dining...
When Indeblue first opened, I didn't like it, and I think it never really took off. But for the past year a very talented chef , Michael Hartzer, (he used to cook at Citronele) took over. I've only tasted one dish of his, it was an Asian-influenced clam hotpot served at a chef celebrity event, but it was excellent, the best dish going up against all the top chefs of DC. I think he is a real talent, but he is pretty much laboring in obscurity. This is a very elegant place that you may be able to get in to on short notice. Maybe the chef would be willing to work with you on menu selection?
At any rate, here is the website, so you can check out the menu and read the bio about the chef:
Based on my personal experiences in their private dining rooms, 1789, 2941, Citronelle, and Inox would be delicious options. Marcel's lower tier would be super if you're willing to go with a semi-private option. (The restaurant is a bi-level space. There's nothing lower tier about Marcel's food or service.) PS7 is a great somewhat lower priced option if the quotes you get from the others I've listed will strain your budget.
777 I Street, NW, Washington, DC 20001
3000 M Street NW, Washington, DC 20007