Maybe it's too early to start thinking of New Year's resolutions, but Kevin Rose (an investor) tweeted that FitStar now has an iPhone app. As far as fitness apps go, this looks nice. FitStar 2.0 is redesigned for iOS 7, has programs that don't require any workout equipment, and has courses tailored to getting you to your desired level of fit, whether it's losing weight, adding tone, or building muscle. A one-year premium membership is also only $29.99 for a limited time, making it much more affordable than a gym membership. Check out FitStar, their programs, and pricing here.
Also worth mentioning: Fitocracy. Fitocracy has some neat ideas around community, gamifying workouts, and also offers various programs from fitness trainers.