I am using the Fitbit app (because I have a fitbit), but I think that app works on its own too. I launch the app to track exercise and it uses GPS and a timer to track distance and speed (even does mile splits). Not sure if the app works like this without a fitbit, but I would think so. And it's free. I also have heard good things about Nike+ apps, and I think they have one for running. I also have Runkeeper on my phone, but haven't tried it yet (it's free too).