I am on Android but they have a similar app for Apple....
Calorie Counter, by FatSecert,
FatSecret iPhone and iPod Touch Application - Calorie Counter, I was doing really well with this before the wife got prego. I was down almost 50lbs, the barcode reader is awesome a must have IMO.
Having been through most of the different apps, this is the one that I liked the best, and have started using again since I am trying to get back on the diet kick.
Did not like:
The only 2 I can think of are the one for the bodybugg and weightwatchers, both were just not good IMO and it has everything to do with no barcode search.