Assuming that you want to design a 2D game, you will need a 2D game engine such as Cocos2D. The engine will take care of all the OpenGL calls, so you can just focus on the design of your game.

A really good book on Cocos2d for iOS devices is this book

You will also need to create sprite sheets for your game. Sprite sheets are used for animation. A good tool to use is TexturePacker.

You will need to add text to your game. To do so, you will need a bitmap font generator such as Glypth Designer,

You will also need to add a Tile Map to your game, so you need a Tile Map Editor such as this one: Tiled Map Editor

If you want to add Physics to your game, then you will also need to download the Box2D framework (or Chipmunk framework)

Thankfully, all these tools have support for Cocos 2D.

And of course, you need a Version Control tool such as Github

These are the main tools that you need to develop a game.

Have fun developing!!!