Beijing Subway guide
At Ethos I needed to design a project to teach OOP to colleagues. We decided to use PHP, since most were familiar with that and used it for work. I settled on finding routes on the Beijing subway as a suitable project: not only does it fit nicely in an OO design, but it is easy to add lots of functionality after the basic part is done. I tested it out by writing my own version of what I wanted.
I have seen similar applications giving the shortest route between two stops, but no other site will provide you with the longest route between two stops.
Try out the Beijing subway route finder.
(update) Or, should I say "Try out the Beijing 2010 subway route finder". The code is easy to update, but getting the coordinates on the map is too much of a hassle, now that there are 3 or 4 new subway lines open. I'll leave this here out of interest, but for anyone who wants to check out subway information, try Explore Beijing's excellent site.