Watch out Hopstop! I wrote a Graph lib in python along with heuristic hSLD A* search and brought it to life with google maps and Ajax. The library is running as a json-rpc service with mod_python. The next step is to use geocoding api to turn street addresses to lat and lon coordinates and integrate it to find starting and ending stations, fun fun fun.
Maybe Ill put this on google app engine if I get alot of hits.