A former Clarendon resident just created an interesting site called Whats The Deal DC. The service is geared towards letting people take advantage of group discounts of local DC restaurants and venues, especially when you don't have a bunch of friends who want to join in on the activity.
Its a good concept: The site negotiates group discounts with local venues. Anyone can sign up for the discounted rate, and if they get a minimum number to participate everyone gets the special deal. If not you don't get charged.
Currently the deal is for a cheaper dinner at Leftbank. I'm following them on twitter and am looking forward to using the service!