Depends on what your limit is and where you are. I can second Founding Farmers for a nice but cheaper dinner. Very loud happy hour feel.
Marcel's is my favorite in DC but it isn't cheap. Food is sensational.
BLT is very nice. Joe's Seafood and Stonecrab (think Truluck's) may be my second favorite in DC. The Palm is nice and always hopping. Couple in Georgetown that names escape me right now off of Wisconsin that are nice. Restaurant in The Mayflower is good as well. Greek fish place around 17th and I is also good if that is the flavor you are looking for.