If you want a peaceful day out of the busy city, Highgate doesn't really feel like London. The cemetery is interesting and peaceful, there's a tour of the old half which is definitely worth the money. Karl Marx, among others are buried there.
Sometimes when I wake up it feels like I am at sea watching a big ocean liner pass by. It is the view from my home in one of the two stepped concrete apartment blocks that make up the Brunswick Centre in Bloomsbury. When you visit skip the chain stores of the shopping centre below (except for the excellent Renoir Cinema) and instead get an invitation to one of the small but gorgeous flats with their winter gardens or just wander through the spectacular concrete A frames and across the vast sun drenched terraces on podium level.
Great little independent bookshop in central London run by Tamsin Clark. Weird and wonderful selection of photo books, magazines, artist books, poetry and more.
The Party Superstore was/is my absolute favourite London shop until it was bizarrely attacked and gutted during the summer London riots. They have been since adopted as a concession by the local Debenhams but you can still savour the full delights of the products and nonsense on line.