What are the best London walking tours?

[WhatsinAname1]

I'm going to London for 4 days. It will be my first time. What walking tours should I take? Is there a website that gives more info about the walking tours?

 

[CmmOlmmm]

Where to in London you going to?
South East London, Waterloo area is the best, because that's where Big Ben, London Eye is.