I often find myself travelling short distances by London Tube and so the Walk It site is becoming more and more useful to me. Basically, instead of travelling the one or two stops between meetings by tube it can often be quicker and healthier to walk - distances in between London Tube stations can be geographically quite small - and even if it is not quicker just getting back out on to the streets and in to the fresh air is better all round. They are even now developing pollution-aware walking routes for the inner city area.
Walk It covers London, Newcastle, Birmingham & Newcastle/Gateshead although I have only tested it in London so far. It shows you the A to B mapped route to walk along with likely journey times at various average walking speeds and the calories you are likely to burn.
What a good idea.