I use a lot of apps in the kitchen. I can never have enough recipes in my database. I'll list a few I use the most and why.
Epicurious- smooth running app, lots of inspiration for recipe creating/menu planning. Very thorough searching feature to find exact recipes from time to cook, what course, dietary considerations, season or occasion
Recipe by Ingredients- a good tool for finding recipes from a list of ingredients although most food apps have this feature, this one is fast to use on the fly.
Allrecipes- A very comprehensive database of recipes with good search results.
Foodgawker lite- very good for inspiration on all types of food trends, picture based browsing and sorting results by category.
Allthecooks- great for finding homespun recipes
whole foods market- nice collection of trendy recipes.
If you only get two apps I would suggest Epicurious and Allrecipes. They each offer great features and pick up where the other lacks in types of recipes. Hope this helps!