Stanford University has offered a wonderful course in iPhone Programming for free online through iTunes U.
It's a great series of lectures, sample applications, and documents that are very helpful for developers who are already familiar with the basics of OOP. It provides a very solid foundation for learning how to develop iPhone Applications.
To get the coursework and videos, go to: CS193P - iPhone Application Programming
We're not sure how long these resources will be available. Get them while you can!