Here's one I liked. NEXERCISE. First of all, and perhaps most importantly after we've all just bankrupted ourselves for the holidays, it's FREE. That's awesome. And it's aim is to help you lose weight by making the journey fun and motivating. It's app blackmail at its finest -- it motivates you to exercise more consistently by using your smartphone to deliver an engaging game, automated tracking, a social support network, and real rewards.
They also have some testimonials on their website that are pretty hard to ignore -- people with high blood pressure getting off their meds, diabetics with amazing bloodwork results, and people losing pounds, dress sizes, and pants sizes.