This is the wrapper for box2d + cocos2d I use in my own game projects.
It is design to work with my PhysicsEditor to create the shapes: http://www.codeandweb.com/physicseditor
To get started check out the tutorial I wrote for Ray Wenderlich's Blog:
It teaches you how to create a complete game from scratch for iOS
It's not yet complete - e.g. joints are not yet supported.
GBox2d is now updated to work with cocos2d 2.0 release with the provided box2d
The MonkeyJump tutorial will be updated to cocos2d 2.x soon ;-)