Google Maps now has real-time traffic displayed and will re-route you if it can:
http://googlemobile.blogspot.com/2011/03/youve-got-better-things-to-do-than-wait.html
It's showing some traffic hotspots in London, so it's a start.
http://googlemobile.blogspot.com/2011/03/youve-got-better-things-to-do-than-wait.html
It's showing some traffic hotspots in London, so it's a start.