You've heard of XML feeds being consumed into a Service Bus - now here's a consumable Bus Service XML feed. The Boston-area MBTA provides a real-time Web Service feed. For example, this request returns an XML document containing details of current locations of the 39 bus which runs from Jamaica Plain to Boston's Back Bay:

http://webservices.nextbus.com/service/publicXMLFeed?command=vehicleLocations&a=mbta&r=39&t=0

As befits a transport organization in for a catchment area which includes MIT, the MBTA has a pretty impressive developers site. And, for anybody keeping score, Boston got there ahead of New York (whose MTA now also provides data feeds).

The MBTA data also has generated some impressive visualizations - check out A Day in the Life of the MBTA.