I've been happy with these apps for my iPhone 4 and think you'll enjoy them too.
New, healthy habits supported by technology and the Internet. Cool!
Improve breathing for relaxation and self-control with Breathing Zone - Relaxing Breathing Exercises (iTunes link)
To improve sleeping and wake gently: Sleep Cycle alarm clock (iTunes link)
Track your runs and rides and walks with RunKeeper (iTunes link)
Keep track of all the weight you're losing with the beautiful Weightbot - Track your weight in style (iTunes link)
Scan good barcodes to learn more about what you're buying with Fooducate (iTunes link)