Restaurants
Italian- Go to the North End- many great Italian restaurants, including the original Pizzeria Regina, which is very good. Gotta go to Mikes Pastry for Dessert. Also, Santarpios in East Boston right near the airport is some of the best pizza I have had, it is a little whole in the wall but you won't be disapointed.
Todd English's Olives is a great choice as well, along with Maggiano's and a couple of the seafood places that have been mentioned- try out Quincy Market by Faneuil Hall during the day, they have a ton of different restaurants inside.
For Chinese, gotta try out The Golden Temple in Brookline- very nice restaurant, excellent Chinese food, and a little more upscale for a Chinese restaurant
For Sunday Brunch, Henrietta's Table is awesome- only been there once, but one of the best brunches. Top of the Hub is also a good choice