Tours: If you don't feel like splashing out on one of the commercial bus tours, you can make your own bus tour by buying an Oyster card and spending some time riding around London on the top deck of standard London buses. Of course you don't get the open air or the commentary, but the views are very similar. You will likely get lost but that is half the fun; if it worries you go for a commercial tour.
Tally Ho! Cycle Tours: 10:30 and 2:30. Guided tours of London's famous landmarks atop a classic 1920's style handmade British bicycle. Stops include Big Ben, The Houses of Parliament, Buckingham Palace, Trafalgar Square and Covent Garden, meandering through backstreet's and cycle paths. An extended tour to Hyde Park and Kensington Gardens for those who are wanting a longer tour. Bicycle hire and private tours also available.
For the first time visitor: see all the major sights - Buckingham Palace, St Paul's Cathedral, Westminster Abbey, Big Ben and the Houses of Parliament, the River Thames and the Royal Parks, Trafalgar Square, Piccadilly Circus, the Horse Guards, the Changing of the Guard, Tower Bridge, the Tower of London and the Crown Jewels. Also see the City, the original site of London, with the Bank of England and Guildhall.