Fitzbillie's is a nice lunch place plus a good bakery. At the high end is Midsummer House where I have not personally dined, but check out the search box above and I think it's been talked about here in the past. Just type in Cambridge and quite a few ideas are bound to show up.
Le Gros Franc is a delightful -- and delicious -- French bistro in the evenings. For pub food, the Eagle and the Anchor are two good choices near King's Parade. De Luca Cucina is good for Italian food, while Aromi is good for sandwiches and pizza.
You should also walk the path to Grantchester for Sunday dinner at the Blue Ball, and for tea at the Orchard.