Moves is an iOS app that tracks your physical activity through the course of the day. It keeps track of mileage, steps, and the amount of time you are engaged in a particular activity. It can also determine the type of activity you are engaged in, for example distinguishing between running, walking or cycling. No need to turn it on say before a run or bike ride, it just runs in the background and figures out the type of activity you are engaged in and tracks it. If by chance it doesn't quite get it right, you have the option to change the type of activity logged.
I've been using it for a few weeks and am finding it useful to keep track of my activity and somewhat motivating too.