After playing Rovio's new Amazing Alex game for a while, and seeing this article on BGR this morning, it made me remember some old success stories that I had read about, and I got to thinking about what it would take to develop a game for iOS. More just to see what options were out there than anything else; I know nothing about game programming. Side note: Amazing Alex is great. If you have ever played the incredible machine, you'll feel right at home.
One success story I remember is Ethan Nicholas and iShoot, which made him over $800k. Check out how he did it, and how to get started with iOS here: iPhone developer in eight easy steps. If he can do it... why not? But, I digress. ManiacDev has great lists of both Open Source and Commercial graphic engines for iOS. As far as free goes, cocos2d and sparrow both jumped out at me. Sparrow seemed like the fastest ramp-up time and after a quick look at it's api, felt familiar. Without diving too much into the examples, it seems to follow similar patterns to some of the python/js UI frameworks I've used. Unfortunately, the forum seems pretty sparse. Cocos2d, while looking like a steeper learning curve, seems a little more mature and a much more engaged community. It's forum has 85% more posts than sparrow, which coming from a busy php/python community, I like to see. As for commercial engines, after reading about how Infinity Blade was Epic's most profitable game ever, and seeing that a license would only be $99, the Unreal Development Kit For iOS is totally the way I would go.