How to be an XCoder is a free open-source book by Bert Altenburg, Alex Clarke and Philippe Mougin that will help you learn Objective-C and Cocoa with Xcode. If you have ever had any interest in writing desktop applications for OSX, this may be a good place to start. This extensive tutorial assumes no prior knowledge of programming, so it might be terrific for a young person you know who has expressed an interest in programming for Mac.
The book is also offered in several different languages and looks to be updated fairly frequently. Again, this may not be very interesting for established developers but for someone just starting out looking for a low-cost way to get some good quality programming education on OS X, this might be it.
