London Eye:
This is the world's largest observation wheel and allows a spectacular way to take in over 55 of London's most famous landmarks in half an hour! One can combine the London Eye Visit with a 40 minute circular cruise on the Thames river. On departing from the LondonEye pier the guided commentary tour takes one from the Houses of Parliament to the Tower of London and back to the London Eye.
London Eye Tickets can be bought from VisitBritaindirect in the form of vouchers and redeemed at the entry.
London Eye gives an excellent view of the city as you can see from the videos here.