I use a app called rxremindme, its a great reminder program for taking your meds and insulin. the app gives a running total of how much insulin is left in your pen and you can set up 'as needed' doses for adjustments of insulin etc.
The Calorie King app is available for iPhone now so grab that if you haven't already.
I'm also a fan of Ayogo's Diabesties. Admittedly I work there, but it's very easy to use, connects you with friends and is free.
Ayogo is also working on some apps for kids. :)