The best travel and commuter apps for iPhone: London Bus Live Countdown

Free
Download from the App Store
If you travel around London chances are you need to use the buses, at the very least it's a scenic way to get around town and discover points of interest you might otherwise miss. London Bus Live Countdown uses data directly from Transport for London (TFL), the local government body responsible for the capital's transport, to take the guess work out of when buses are due to arrive at your stop. Users can also find local bus routes using the iPhone's GPS function, explore maps and check which routes may be cancelled or delayed.
For those will Oyster travel cards, the app also displays your balance, a useful reminder for when you need to top up. The only real niggle here is that the data supplied by TFL is occasionally not available, due to maintenance work.