http://www.bignerdranch.com/products/cocoa1.shtml

'Cocoa Programming for Mac OS X (2nd Edition)' by Aaron Hillegass is a comprehensive guide to writing Cocoa applications. The book takes a very practical approach, based on the courses taught at the Big Nerd Ranch, with a large amount of example code.

The second edition adds a number of new chapters, and is considered by many to be a must-have book for Cocoa developers.

http://www.cocoaprogramming.net

'Cocoa Programming' by Scott Anguish, Erik M. Buck and Donald A. Yacktman provides intermediate and advanced Cocoa developers with knowledge and techniques to create full-featured applications.

While the book doesn't cover anything after Mac OS X 10.2, the content is still highly recommended and relevant. A wide variety of topics are covered in detail, which explains the 1,000+ pages!

http://www.oreilly.com/catalog/buildcocoa/index.html

'Building Cocoa Applications, a step-by-step guide' by Simson Garfinkel and Michael J Mahoney takes, as the title suggests, a step-by-step approach to the construction of a Cocoa application. In this case the examples MathPaper and GraphPaper cover topics from basic application constuction to mouse tracking and multi-threading.

http://www.oreilly.com/catalog/cocoaian/

'Cocoa in a Nutshell' by Michael Beam and James Duncan Davidson is divided into two parts: the first is an overview of frequently-used Cocoa classes, while the second is a detailed quick reference to the Foundation and AppKit classes.

While it is useful having this reference in a concise printed form, the book only covers up to Mac OS X 10.2 Jaguar.

http://www.oreilly.com/catalog/learncocoa2/

'Learning Cocoa with Objective-C, 2nd edition' by James Duncan Davidson, provides an introduction to Cocoa development through the use of Project Builder and Interface Builder; an introduction to Objective-C; and a series of examples based on Apple sample code.

Given that Project Builder has been replaced by Xcode, and that the content is based on Mac OS X 10.2 Jaguar, parts of the book are now dated but the key concepts are still relevant.

http://www.oreilly.com/catalog/learncocoa/

'Learning Cocoa, 1st edition' by 'insiders at Apple Computer with access to engineers deeply involved in creating Mac OS X' was not very well received by the Cocoa development community as almost all of the content was already available on the ADC site.

On the positive side, it was nice to have it in printed form, and it was given away at WWDC 2001.