If you bake, then you know that it is a science. Experimentation with a recipe may lead to disastrous results. Here are two useful apps, Ratio and Food Substitutes, that are recommended by Dessert Professional, a trade magazine for bakers and pastry chefs.
Ratio: Michael Ruhlman, chef, author and blogger, has an excellent iPhone, iPad and iPod Touch app that will help you calculate amounts of ingredients in all the fundamental culinary preparations. This app is actually based on his book, Ratio: The Simple Codes Behind the Craft of Everyday Cooking. The ratio is a good tool for scaling recipes for big scale baking or for catering. $4.99
Food Substitutes: Created by Phoxware, this app helps you find alternatives to ingredients in a recipe. This may save you a trip to the grocery or help you discover a new elements to use in a dish. The app is available on iPhone and iPod Touch. $2.99