Not the most exciting place inside, but a lovely rooftop area which not all that many people seem to know about, 2 mins walk from Old St station. If it's packed then The Red Lion is just up the road.
The Almeida, in Islington, is a small theatre with big influence. It's an intimate place to discover groundbreaking theatre and get up close to some of Britain's leading actors. The cafe/bar across has a constantly-changing tasty menu, relaxed atmosphere and free wifi. Open all day and great place to spend time even if you're not going to catch a production.
Zédel is my absolute favorite restaurant in London. Beside the fact that I love french cuisine, Zédel is aesthetically pleasing, very reasonably priced, is good for any occasion, and of course - delicious. My favorite is the bouillabaisse and a bottle of the Bordeaux Superior.