I currently use Islet for my iPod touch.
It's a fantastic and simple app that tracks glucose, insulin, carb intake, and exercise. You can even email the data to yourself for printing out.
It even graphs the data which you can save as a picture in the app and then also email that to yourself, or whoever.
Data entry is incredibly easy and you can customize the types of insulin you take and easily select which one you are giving to yourself when you enter the units.
All in all, it's a great application and it's rock solid, has great support, and is only $2.99. I think it's a lot better than a lot of the other diabetes apps on the App Store as it doesn't try to do a lot of things like ridiculously inaccurate food databases and other bloat features. Islet keeps it simple and stable, and it really makes keeping track of my diabetes something that I enjoy because of the simplicity.
It's second nature to have my iPod touch right next to my meter when checking my glucose, and it feels really good to know that by documenting all of this, I am staying on top of my diabetes.
You can buy Islet by going here for a link to the App Store: http://itunes.apple.com/us/app/islet-diabetes-assistant/id294770449?mt=8
Hope that helps! Good luck!