Having read their Cocoa programming for OS X book (http://www.amazon.com/Cocoa-Programming-Mac-3rd-Edition/dp/0...), I can wholeheartedly recommend their books.
It's probably best to start with a small project and tackle one project after the other.
I also read this book which helped since it tackled all the basics that one needs to know for a full Mac app. It's german only though (http://www.amazon.de/Objective-C-Cocoa-Nachfolger-Tiger-XCod...) alternatively the aforementioned Hillegas (http://www.amazon.com/Objective-C-Programming-Ranch-Guide-Gu...) which is really good.
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