Epicurious (free) - I'm very surprised that so many people have given this app one star in iTunes, because it is one of my go-to resources when I am looking for something new to cook. While it does have a lot of advertising, which seems to be the reviewers' main issue with it, it is a free app that is a wealth of information. It also has some great features that (in my mind) more than make up for the ads. One of my favorite features is the sections that correspond to the seasons (like Spring Breakfasts or Holiday Recipes), and the search feature gives you a lot of options to find a particular type of recipe. For instance, you can search by main ingredient, meal/course, cuisine, dietary consideration, and/or season. I've found a number of excellent recipes by virtue of random searches. My two favorite finds are strawberry citrus salad and lemon-glazed butter cake.
How to Cook Everything (full version $4.99, essentials version is free) - I am a Mark Bittman fangirl, so it isn't surprising that I find this app so useful. While I typically use the actual cookbook when I am cooking, this app is perfect to reference while in the grocery store (or on the subway) when I need to go shopping or when I need some inspiration for dinner. This app also was a lifesaver when I found myself in the role of the reluctant chef for a dinner party at my mom's last year. If I ever have to make hollandaise sauce ever again, I hope I have this app and Bittman's common-sense approach to guide me.
Evernote (free) - I know that this technically is not a food app, but I tend to use Evernote to clip recipes from my favorite cooking websites. Not only is it an easy way to collect these recipes, I can also categorize them using the tags and notebook feature. What more could I ask for?
What great cooking app did I miss? Please feel free to offer suggestions in the comments section!