Stanford's free app development courses are awesome. If you're interested in making an app for the iPhone or iPad, subscribe to their newly launched iOS 9 course on iTunes U. This is a long-awaited update to the previous iOS 8 course. It covers how to use the iOS SDK and Apple's Swift programming language, as well as principles in app design and development. Currently, only one video is available and the outline isn't complete, but you can get lectures as they're released if you subscribe to it in iTunes.
Developing iOS 9 Apps with Swift [iTunes U]