Update (Jan 7): Apparantly the City of Ottawa has suspended open access to the OC Transpo GPS data that this app (and others like it) relied on to provide the info. Could be a few weeks until it's back online.
Earlier this month a new app launched called Where is my bus?
It was created by Jonathan Rudenberg as an entry in Ottawa's Open Data App Contest. He tells us: "As part of the City of Ottawa's Open Data initiative, OC Transpo has given me and a bunch of other developers access to a live feed of GPS locations of buses. Using this data, the schedules are updated in realtime, so that the arrival time reflects if the bus is delayed/early. It is quite a bit more accurate than the printed schedules, normally within a minute of the bus arrival."
Related: Ottawa OC Transpo Guide