Chris Miles with a port of the $1 Unistroke Recogniser completely encapsulated in a UIGestureRecognizer. Easy to use too, all that is needed is a path with the shape you want to recognise passed to the recogniser. The demo works really well and when I looked there was a surprisingly small amount of code in the recogniser which is testament to both Chris and the original authors of the algorithm.
Interesting library from Zynga which could really help out if you are splitting code/functionality between a native app and a web view. For example, physics engine in native code controlling objects in a web view DOM.
Fun experiment from Wade Cosgrove of Panic on recreating the algorithm used in iTunes 11 for determining effective UI colours from Album art. I wonder if we will see an explosion of this being used in iOS apps now that iTunes 11 has provided a bit of inspiration.
I wrote my first non-trivial UICollectionViewLayout subclass recently and so I was really pleased to see this tutorial by Bryan Hansen published this week. It is a fairly comprehensive, step by step look at building up a collection view with a custom layout. Useful if you haven't tackled one yet.