There is no shortage of grocery list apps and kitchen calculator apps, but here's an example of each that I think iPhone owners might find useful.
The first goes beyond simply helping you create a shopping list for your next run to the store. In addition to creating a grocery list, it also helps you schedule and plan your meals. The second app is noteworthy because it provides useful kitchen conversions and substitutions for free.
Mise En Place
I have yet to find a grocery list app that is easier to use than the small pad of paper I keep on my kitchen counter. Mise En Place (the French term for the gathering and arrangement of ingredients before cooking begins) is only partly a grocery list app. At the heart of the app, it helps you schedule and plan your meals.
To get started, tap the Plan button from the bottom menu bar and then tap the plus-sign button in the upper-right corner. Enter the name of the dish, the cookbook or Web site where you found the recipe, and when you plan on eating it. You can then add tasks involved in preparing the dish and create a shopping list for any ingredients you don't already have in the house. When creating a task, you can either manually set the time or use the schedule wizard to plan a task a certain amount before (or after) mealtime.
Below the tasks for a particular dish on the Plan screen, you can create a shopping list. You pick items from a master list, but if you need something that is not listed, tap the Edit button and then the plus button to add an ingredient to the master list. You can also delete items from the list using the Edit button. When building your shopping list, you must enter a date for when you need to buy an item, and you have the option of adding the amount needed of each item.
It's convenient to have a shopping list for each dish, but if you tap the Shop button from the bottom menu bar, you can see all of the items needed for Today or All (which groups items by day). You can also add to your grocery list from the Shop screen, if you need a staple that isn't tied to a particular dish.
Tap on the Check button from the bottom menu bar and you get a daily view of the dishes, tasks, and shopping needed. You can also add a dish to a Favorites list by tapping the star at the bottom of either the Check screen or the Plan screen. Your favorites can be found by tapping the More button from the bottom menu bar. Lastly, the Scribble button presents a blank page where you can type notes to yourself. Unfortunately, there is no way to tie a scribble to a dish, if you wanted to remind yourself to double the recipe or adjust the ingredients in some way.
Merillat Kitchen Helper
There are a number of kitchen calculator apps that tell you how many fluid ounces are in a cup or how to convert tablespoons to cups. The thing is, for this simple service, the answers of which are only a Google search away, they insist on charging you a buck or more. In Merillat Kitchen Helper (also here on iTunes), I finally found a free app that provides useful kitchen conversions. It also features a deep list of substitutions.
The app is dead simple to use. Tap the large Conversion button and you'll see a list of common conversions, from 1 pinch = 1/16 tsp to 1 pound = 454 grams. If you don't see what you are looking for here, tap the Convert button in the upper-right corner and you can enter your own liquid or dry measurement conversion. There is also a helpful slider that converts degrees Fahrenheit to Celsius.
The Substitutions section can be navigated by category or by searching, and for each substitution listed, the app provides a Change Quantity button to get you the information you need. Next to each substitution is a star, which you can use to mark it as a favorite, creating a handy list of your most-used substitutions.