This isn't an app per se, but I don't think it's off-topic. My wife has a MOTOACTV, and it is an excellent device. It's usually spot-on with the dedicated running GPS's others in our group have, it has a great display with big numbers and a lot of customization. Being able to sync to the MOTOACTV android app after a workout is cool too, as it shows more info that the wrist unit. We haven't hit distances that cause battery life to be a problem yet, but that's coming later this fall. We also haven't tried it as an MP3 player.
If you're serious about accuracy I would recommend it. I've stopped running with my phone and just let her tell me our distance and pace. ;-) I think Moto is dropping the price, too.