About two months ago, I began investigating the finer points of iPhone and mobile device application development. My search of the internet revealed quite a few really good resources for those looking to get into this sphere of development.
As time goes by, it feels a more and more like development on the old 8-bit computers back in the day. You need to work around screen size, processor, and memory limitations - but you still have a ton more resources at your disposal than the Commodore, Apple II and Atari computers of yesterday. Coupled with the enhanced user interface, accelerometer and other advanced interaction components and you have the basis for a really interesting platform on which to develop.
My quest lead me to a ton of resources, and a handful of really helpful ones. Here are a few just to get us going:
CS193P - iTunes U Class
This is a course taught at Stanford University by Apple engineers on developing for the iPhone. It is a fast-paced, project-oriented class that covers a great deal of basic iPhone functionality including views, table-views, data, graphics and all of the basic elements of iPhone development. They have a LOT of ground to cover in a 10 week class and watching the class lectures can sometimes leave you gasping for air, but there is a lot of really good information in here directly from Apple's engineers. There is no "textbook" for the course, but there are many books out there that can be used to supplement Apple's existing documentation and materials presented in the course directly. This is a challenging course to keep up with, but it is very informational.
Keep in mind that this is a college course, so there are pre-requiste courses. You should have a least a grasp of C++, C or Objective-C before you go venturing into this. I have some C++ experience and still had to spend some quality time dealing with syntax issues.
Beginning iPhone 3 Development: Exploring the iPhone SDK
This should be the book that goes with the course listed above. It takes a little more of a beginner approach to iPhone development. After taking about half the CS193 course, I was able to skip over about half of this book. The information on Core Data was very helpful tho when it came to dealing with those class projects. I'm going through many of the other chapters now as this is a pre-requisite book to the next book I am going to be getting into: More iPhone 3 Development.
More iPhone 3 Development: Tackling iPhone 34 SDK
I've only looked in this briefly, but it greatly expands on the concepts in the first book. I'll be providing more detail on this as I progress through it. Obviously, it covers more advanced concepts and goes into greater detail than the introductory book.
For the iPhone application I am currently working on, I have completed my wireframe and navigation stacks. I am now coordinating with a competent designer so we can make the application look and feel like a quality iPhone app and not just have all my mocked-up wireframes in there! :)