Swiss Trains (http://www.swisstrains.ch) is a real-time mashsup of Google Maps and trains in Switzerland. Hover over the trains and you get the train number, the locations from and to which it's heading, and its speed. Clicking on the train itself will show its schedule along the entire line. Very cool!
I wonder what kind of API they are grabbing these data from, and certainly wish that MTA will structure similar API to New Yorkers, though unlikely all for the sake of 'homeland security'… :(