RunKeeper
Our sister site, The Sweet Setup, picked RunKeeper as their favorite running app for the iPhone. While a lot of runners prefer watches with dedicated GPS units — like this one — the iPhone makes for a great alternative. There are a lot of run-tracking apps, but RunKeeper is our favorite running app due to its deep feature set, vibrant community, and strong integration with other services. I've tracked over 400 runs with it, and even after spending time with a host of other applications, RunKeeper stands apart.