So… Are you an experienced programmer and is moving to Cocoa? For either MacOS X or iPhone OS, the Cocoa Programming: A Quick-Start Guide for Developers book from the Pragmatic Bookshelf is a great addition to your library. It’s a great deal, wich i’ve just finished reading. The eBook costs $22.00 (US Dollars).
It assumes that you already know how to code, and is moving to a new platform (in this case Cocoa). It helped me a lot (and it still does) when I came from my C/C++ background to the MacOS Cocoa + ObjectiveC. It’s a hands-on approach that leaves no gaps in the explanations. I’ve found myself many times coming from the Apple’s official tutorials to the eBook to get some clarification on some topics. It’s great both for learning and for reference.
If you’re new to programming and is starting in a MacOS platform, you can check out the Beginning Mac Programming: Develop with Objective-C and Cocoa. I haven’t read this one, but it seems to make the same approach from the first one, except it does not assume any programming background.
In the meantime, my wishlist is available with some other options of books (and, if you want to send me a gift, those are great ones).