There are several good tutorials about iOS. Here I want to make summary some of them:
Stanford - iPhone application development - 5/5
This is might be the best tutorial in the Internet. You can download very good tutorials from iTunes:
Oct 2010: http://itunes.apple.com/us/itunes-u/developing-apps-for-ios-sd/id395631522
Winter 2010: http://itunes.apple.com/us/itunes-u/iphone-application-development/id384233225
Fall 2011: http://itunes.apple.com/es/itunes-u/ipad-iphone-application-development/id480479762
and the pdf and the programs used from here:
iOS Developer:tips - 4/5
A great web page with many tips to code iOS. They come with examples and even the code to used the examples and the outputs.
Ray Wenderlich - iPhone tutorials - 5/5
There are many tutorials sorted by difficulty. Really great to practice the theory learned from the videos of Stanford.
Cocoa Dev Central - Learn Object C - 3/5
Basic tutorial to deal with Object C