Two new trip planners for pedestrians, cyclists an motorists have be launched in the UK in the past few months, both based on OpenStreetMap data, and both offered without charge. The software for both projects is likely to be made open source.
OpenRouteService was developed at the University of Bonn and uses the new OpenLS services published by the Open Geospatial Consortium. It was launched in Germany in May 2008 and coverage was extended to cover the UK and Ireland early in September 2008.
The Your Navigation service was was also launched in the UK in September 2008. Using both services it is possible to select a start and end location and a mode and the service will calculate a suitable route.
Here is YourNavigation for a walking route in central London.

Walking route in central London
And here is the same route by bicycle:

Bicycling route in Central London
And by car:

Driving route in Central London
OpenRouteService is able to offer similar functionality but can also use real time (TMC) traffic data for the Northrhine-Westphalia and Bavaria areas. The image below shows two areas of traffic congestion in the Cologne area..

Traffic in Cologne
The static data on which this is based is collected by volunteers for OpenStreetMap and is available on a Creative Commons Licence. The OpenStreetMap community is currently improving the tagging of road and path data to improve the accuracy of the routing. Coverage for OpenStreetMap is expanding fast in the UK and elsewhere.