Map My Run is an app that I use whenever I go running.  It allows you not only to keep track of your running history, but also how many miles you have completed within any given run.  Beyond that, it recommends different routes depending on your desired distance.  As someone who really loves to run, it enables me to explore without feeling lost, and to keep track of any progress I am making.  Any one of its functionalities would have made it a desirable app, but the combination is truly great.