I picked up a couple books the other day that I am quite impressed with for developers wanting to learn Objective-C, Cocoa, Xcode, Interface Builder and development for the Mac, iPhone, and iPad.
The first book is: Beginning Mac Programming. This is a good starter book for those developers who are completely new to Xcode, Interface Builder, Objective-C, and Object-Oriented Programming. This has a lot of good OOP fundamentals for those who are completely new to programming and the C Language. If you are an experienced programmer with OOP experience and background in a C language like C#, it may be a little slow and drawn out in spots teaching you stuff you may already know. Still, the Xcode, Interface Builder, and coverage of Memory Management will still be worth it.
The next book is iPhone and iPad in Action. This books wastes no time teaching you the fundamentals of iPhone and iPad Development. It quickly, and I mean quickly, gives you an overview of Objective-C and Cocoa before diving into Xcode and Interface Builder and creating your first iPhone applications. Luckily I had been reading Beginning Mac Programming which filled in the holes as the book really expects some fundamental knowledge. I am only 1/4 through the book, but iPhone and iPad in Action is a real winner. It does not waste your time and starts teaching you development while giving you just what you need to know about Xcode, Interface Builder, Objective-C, and Cocoa along the way. It feels intense as a newbie to iPhone and iPad development, but I appreciate the boot camp, no nonsense approach.
David Hayden