- Concepts in Objective-C Programming and Cocoa Core Compentencies – Apple’s official basic documentation for the language and the Cocoa framework.
- Cocoa Programming for Mac OS X – The definitive book for Cocoa newcomers. It’s actually focused on the Cocoa frameworks more than Objective-C, but still invaluable.
- Programming in Objective-C 2.0 – Focuses on Objective-C itself more than Cocoa; may have more basic information than an experienced programmer would need, but covers plenty of good stuff.
- The “Language” part of Matt Neuberg’s Programming iOS 6 covers Objective-C itself in detail.
- CocoaDevCentral – Excellent tutorials. Start with the “Learn …” and “Objective-C Style” tutorials.
- Stanford’s free CS193E and CS193P courses
- CocoaHeads.org – A large list of resources (books, website, and code) about Cocoa/Objective-C.
- HyperJeff’s Cocoa Literature List – A huge compendium of useful information, etc.
- Cocoa With Love – An excellent blog with specific, useful snippets and in-depth explanation.
- Cocoa Is My Girlfriend – A fun and useful blog (usually) about Cocoa.
- Best Practices for Cocoa Programmers (by Aaron Hillegass) – A bit dated, but contains some nuggets and guidelines for understanding and following Objective-C/Cocoa conventions
- CocoaDev.com wiki – Especially good for specific questions about a specific class or task. (Undergoing updates.)