The two old hotels are wonderful for "romantic" quiet dinners (Oak Room & English Grill). For newer, Eddie Merlot's can be great, as long as you don't have a huge party nearby. Sometimes if we really want to talk we'll hit Simply Thai early, for a quiet booth against a window. Buck's is always good for talking; they do have live music on weekends, but it's quiet. Wild Ginger sushi is usually quiet and relaxed.
Peking City and Z's Fusion can also be quiet.
With every restaurant listed, having a big party nearby can destroy a mood with loud noise (as Robin indicated for 610), but you always have that risk when dining out.