Stanford is currently offering in iTunes U their Winter 2013 iPhone Application Development class. The course is currently five or six lectures in, but since folks not enrolled at Stanford can only audit the class, I think anyone can just jump right in.
And get lost.
The instructor runs through a list of prerequisites that included three classes offered at the university: CS106, CS107 and CS108. iTunes U may have notes from the classes, but not all the videos. The first two classes, however, have archived lectures on YouTube, however they may not be in synch with the video content. The class site mentioned in the CS1o6 course is synched with the current semester.
The CS193P class dives right into Objective C and makes all kinds of assumptions on the students, like they are familiar with programming and are already comfortable coding programs.