jQTouch is a jQuery framework for building iPhone web apps. Of particular note is the way it handles transition animations:
It is important to note that all animations are handled with CSS3 and classes. [...] Adding your own animations is straight-forward. Just add the corresponding class definitions (using CSS3 keyframe animations), and add the animation with the corresponding public function.
CSS3 animations dramatically outperform traditional Javascript animation methods on the iPhone’s limited hardware.