I use Carbs and Cals app, it's also backed by my local hospital. I find the photos of the portion size helps as it is easy to use in restaurants etc... And you don't need to worry about weighing your food etc[/QUOTE
I agree the carbs and cals app is brilliant, there is also a carbs and cals book it is produced by Roche.
I find google pretty good too, just put in carb value of medium green apple for example and you'll get loads of sites but you have to look around for the good ones.
My fitness pal is a pretty good site too.