Zombies, Run! works under the premise the city you're running across is filled with the brain-eating undead, and users are fed an audio narration revolving around post zombie apocalypse missions (collect water, food, medicine). It's one part audio book, another part video game, and a sly personal trainer, combining all three elements to create an entertaining workout which makes you forget you're actually working out. Fans of The Walking Dead looking to get exercising/motivated again seem to love it, as proven by all the IMs and emails from friends asking me if I've tried it out (unfortunately not, because I'm on a Windows Phone). Maybe I'll need to borrow an iPhone soon.
I'm an on and off runner (several 5K and 10K's and a pair of half marathons on my short running resume are countered by a lax commitment these days), and personally not drawn to the undead personal training route, but as someone who has used Nike+ and social running sites like Runkeeper and DailyMile to keep tabs on my progress, I can recognize these sort of fun motivating tools are nothing to dismiss. If a zombie app gets someone motivated to get up from off their duff, even if because their running away from imaginary undead, I'm all for it (personally, an iPad Nano and its built-in pedometer is enough tech for me to lug around).
If zombies aren't your thing, the Nike+ Fuelband offers possibly the most advanced, consumer-oriented fitness tool. Because let's be frank, sometimes it's new equipment which motivates us back into the gym or out exercising. The three-axis accelerometer LED bracelet tracks time, distance, calories, and taps into a similar competitive streak without utilizing the undead as motivation. The Nike+ website works in conjunction, providing visual feedback and motivation to keep at it (consistency, not distance or speed, is the making of a good runner!). I've used the Nike+ shoe sensor with the accompany site to train for races, and it's proved to be useful for an everyday, normal (aka slowpoke) runner like myself, and this band seems like an even easier way to keep tabs about activity rates throughout the day, albeit an expensive one.
An even more basic workout monitoring app is the $1.99 Streaks. It's a bare bones, but visual informative and attractive goals calendar app. The premise is simple: keep the streak alive. Every time you run, mark down the day on the calendar, and you've got the digital equivalent of the calendar on the fridge.