On this page I will try to list resources I have found useful when learning about iOS.
Learning Objective C
Learning Objective C: A Primer If you are already familiar with C or C++ programming this is a great introduction to the Objective-C syntax.
Object-Oriented Programming with Objective-C If you are not familiar with Object-Oriented Programming this is Apple’s introduction to the subject. Despite the title, it is rather language neutral. On the down side it is rather heavy on terminology.