Originally Posted by EdV
Grille 23 on Berkley st will give you a nice restaurant experience, good food for you and eas(ier) on your wallet.
I'm a fan of Grill 23 -- it's where I go when I want steak in Boston -- but the atmsopehere is mens clubby and I think it's in the same general price range as the other places recommended.
For a nice but more casual restaurant, consider the Bristol Lounge at the Four Seasons Hotel. It is the more casual of their two restaurants, but it still is a lovely place with very good food. If you tell them about the special occasion, you might be able to get one of the tables in the window looking across to the Public Gardens