Ray Wenderlich and his team of iOS developers/writers have put together an impressive collection of tutorials in their lastest book iOS 6 by tutorials – available in PDF and print.
It all started so simple 4+ years ago. However, the iOS platform has become quite comprehensive, and with each new milestone release of iOS comes an abundance of new features. It can be quite a challenge to keep up. iOS 6 by tutorials covers many of most recent additions to iOS 6 including UICollectionView, Auto Layout, Passbook, among others.