London restaurants and things to do

Hey -- in London for the first time ever so I'd love some suggestions on good restaurants and also solid places that are relatively cheap (also for Paris Barcelona and Istanbul haha) although I've noticed in Europe the eating out price is quite rapey compared to the states. Just landed from Iceland where I was at the blue lagoon and ate at the Grillmarket -- staying at the edge between green park and Hyde park and walked around James oxford and Baker street today! Thxthx