One of the best ways to see London is to take a guided tour of the city. Below are some links to tour websites.

http://www.theoriginaltour.com
This company has been operating for almost 60 years and conducts tours on a double decker bus. They also offering walking tours and river cruises.

http://www.londonducktours.co.uk
This company offers a tour of London by both road and water. They use a special vehicle which can travel on both land and water.