If you're looking to get into iOS app development, you have a lot of free options available to you, but few are better than Stanford's online courses. The university has just released its newest course, which tackles Apple's new Swift programming language, and it's available for free.
The course digs into iOS 8 and Swift, as well as covering interface design, animation, power management and more. You'll need to know at least a little about C before you dive in (which you can also learn for free), but otherwise it's all about Apple's language.
Developing iOS 8 Apps with Swift [iTunes U]