The British charity Diabetes UK has put together this app to help make it easier for diabetes sufferers to log their daily levels and more effectively manage their illness. The app allows you to log your blood glucose levels, insulin doses, carb and calorie intake as well as your weight and ketones.
There are graphs to let you visual your results over days and weeks and these can be emailed directly from the app to healthcare professionals. You can also take photos of your meals and make notes on your mood to keep a log of how you've been feeling on different days.
It's not yet perfect, as it's missing some features such as a way to keep a log of any exercise you've done, but this app's friendly layout and decent range of features still make it worth investigation.