Mapnificent is a very cool Google map mashup which shows estimated travel times on public transport for a growing list of the world’s biggest cities. The interface is super slick, just drop the pointer on your starting position, drag the slider to encompass your desired destination and read off the travel time using bus or train.
It copes with bicycle times too, and compensates for the walk time to and from stations. The whole thing is based on a beta project called Mapumental (which shows easy commuting areas for house buyers), but this looks like a much more interesting product all round. Neat.
Mapnificent shows you the area you can reach with public transport from any point in a given time. It is available for major cities in the US and world wide.