Hard to get into 22 or Midsummer House but very worth it. You are more likely to get into Parker's Tavern.
Varsity hotel has a marvellous roof top bar.
Riverside Brasserie is good although I find the Riverside Grill lacking in atmosphere.
The Oak Bistro is excellent.
Galleria restaurant is best for pre theatre food.
Garden House hotel has a nice garden next to the river for afternoon tea. Grantchester Tea Rooms are a tourist visit, very atmospheric.