Tom Steinberg and Chris Lightfoot have put together some interesting and beautiful travel time maps. Tom's post to the geowanking mailing list introduces them best:

The ever-gifted Chris Lightfoot has been writing code to scrape journey planner websites, producing "a solution to Laplace's equation, fixing its value to the value of the travel-time on the boundary of its domain", and drinking coffee all in order to produce these fascinating maps for your delectation.