I’ve spent quite a bit of time looking into different 2d and 3d engines. I came across Cocos2d a while back but have only recently started playing around with it. It’s very nice and well supported. The forum is active and the developers are active. All good things IMO.
“cocos2d for iPhone is a framework for building 2D games, demos, and other graphical/interactive applications. It is based on the cocos2d design: it uses the same concepts, but instead of using python it uses objective-c.”
So far it seems very well thought out and well documented. Well worth a look if your doing 2d games on iOS.
I will post some tutorials on using it soon 😉