Are you staying at either the Copley Marriott or the Westin? If you are, the hotels are connected to two malls. The Copley Place Mall has a lot of upscale stores. There is a covered walkway that connects the Copley Mall to the Prudential Center Malls. There are more restaurant choices over there (Cheesecake Factory, Dick's Last Resort, California Pizza Kitchen, and a great food court--including a brand new Krispy Kreme

).
You can go to the top of the Prudential Center. You can even see Fenway Park from up there.
You can also take a Duck Tour from the Prudential Center. It's a tour of Boston by land and water, and it's a lot of fun.
If you like to walk, you are just a few blocks from Newbury Street, a very quaint street with lots of neat shops and restaurants.
The Christian Science Church is nearby, and there is a really neat walk through globe called the Maporium there. Last time I was there, it was free to walk through this.
If you want to go out for a really good meal, go to Fire and Ice on the corner of Berkley and St. James. It's about a five minute walk from the Copley area (your hotel should be able to give you directions). It's like a Mongolian grill. Basically, you pick out the ingredients you want in your meal, bring it up to the grill, and the chefs cook it for you. It's around $18, and it's all you can eat. Very yummy.
Karen