The "health and fitness" area of the AppStore is filled with extremely bad calorie counter apps (such as "Absolute Fitness" — which should be totally avoided). With the self-proclaimed tagline "Serious Weight Loss Comes to the iPhone", MyNetDiary promises more and delivers.
First of all, this is a combo webapp/iPhone app - a formula i think we will see a lot more of in the future. The website is a great ajax-driven web 2.0 application. Enter a few letters of a food, and the website will find all related food choices — and organize it for you by day and meal. Its easy to go back and fill in entries that you might of missed. At the end of every day, the "analysis" feature tells you how you are doing relative to your plan; the "nutrition" graph breaks down the nutritional value of your diet.
As for the iPhone app — it's also first rate. Entering meals or activities is easy — and the daily Nutrition Summary allows you to easily see if you are above or below plan — and how much more you can eat that day.
I really have nothing bad to say for that app other than the price point — 9 dollars per month, billed directly — as opposed to through the App Store ($7/month if you buy 6 months). But, unless somebody else comes up with a cheaper version of the same functionality, I think anybody seriously interested in weight loss will want to try out MyNetDiary.