There are many different groups that offer tours of London. I can recommend the following:

  • London Walks - If you do not mind walking, this group offers MANY different walks around London (and even outlying areas such as Oxford and Cambridge). Their walks cost £5 and you can get a 'Discount Walkabout Card' which allows you pay one cost for as many walks as you can take in a day (after the Jack the Ripper walk I can't see how you could go on more than two in a day). You will find their brochure throughout London. Walks typically meet at a particular Underground station and last for a few hours. THE way to see London.
  • The Original London Sightseeing Tour/Golden Tours - Hop On Hop Off/Big Bus London - There are many such companies in London that allow you to 'hop on/hop off' their buses to visit most key places in the central London area. Great way to see (in relaxation) the core area. Note: Another, cheaper, way to see the area, though without the commentary is simply to catch a city bus going to some specific area (just look at the front of the bus) – take a city map or guide with you to get the most from the trip.
  • Boat Tours on the Thames - Most leave from Westminster Bridge (near the houses of parliament; TUBE Westminster) and offer a great view of the city. I can recommend the ferry to the Thames Barrier, an extraordinary barrier built to protect London from flooding well east of London. The ferry takes you well past Greenwich (and the much criticised Millennium Dome) and drops you off at the barrier museum. Quite a different trip.

If you want to perhaps splash out a bit, though perhaps not as much as you might think, there is nothing like seeing London from the air try for helicopters tours of the city.

Note: TUBE Indicates closest London Underground station, see Transport for London for further information.