The app How to Cook Everything for iPhone and iPad is free today. I don’t know how long it will last, so if you like to cook, you should go grab it while you can.
The app is based on the book of the same name by Mark Bittman, a columnist for the New York Times. It has 2,000 recipes and 400 how-to illustrations.
This app is really well designed, each recipe links to relevant techniques and has an easy-to-use format for the ingredients and variations.