Windows Phone app Next DC Bus tracks bus arrivals in real time in DC, Virginia and Maryland
Once you select which bus stop you need to get to, the app will show you directions from your current location to that particular stop. The complete route of any bus can be mapped from the current day or for the future. The app will also plot the real time location of a bus that you're on, and will auto-refresh every 60 seconds automatically.
Next DC Bus is not only free, it also has no advertising. If you often ride the bus in D.C.,Virginia and Maryland, this app should help you get to your destination in a timely fashion.
source: NextDCBus via WMPoweruser