Anyone who's visited London is likely to have used many of the available transport options including the tube (underground), bus, train (over land) and possibly the river taxis too. If you visit as a tourist then you may have time to amble around and try the various alternatives - those of you on business are likely to require a speedy way to find the quickest route particularly when visiting an area of London that you're not familiar with.
There are many websites for each mode of transport - the challenge for humble travellers such as myself is that typical journeys may require traversing multiple modes of transport and hence the excellent Transport for London website's journey planner is a great resource.
The beauty of the site is that you can enter your both departure point and destination in terms of the nearest Station, the Post Code, Place of interest, or Address.
The example shown below is one of the suggested routes to travel from London Bridge (Railway station) to Somerset House (a very interesting place of interest that includes an Ice Rink and Ice Wall over the Christmas period).
Of course you don't have to travel by Boat! The Journey Planner presented a series of options - each listed the suggested combination of transport modes - you can choose which you'd like to use when submitting your request.
It's nice to see the common sense option of "walk if it reduces my journey time"! Where walking is suggested you have the option of downloading a PDF file containing a detailed map for the proposed route.