Getting started with Cocoa
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaFundamentals
http://www.amazon.com/dp/0321503619/?tag=stackoverfl08-20
Getting started with Objective-C
http://developer.apple.com/library/mac/#referencelibrary/GettingStarted/Learning_Objective-C_A_Primer
http://cocoadevcentral.com/d/learn_objectivec/
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC
AppKit
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/AppArchitecture
Blocks (closures)
http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/Blocks
Objective-C Garbage Collection
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/GarbageCollection
Sample Code & Tutorials
Basic Cocoa & Graphics
/Developer/Examples/TextEdit
/Developer/Examples/CircleView
/Developer/Examples/OpenGL/Cocoa/GLImageWall
http://developer.apple.com/library/mac/#samplecode/CoreAnimationKioskStyleMenu
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreAnimation_guide/Articles/Headstart.html
Free Videos on iTunes
2007 Mac OS X Platform Overview
2008 Intro to Mac and iOS Development
2008 Getting Started with Objective-C: Coming from Other Languages
2008 Cocoa Fundamentals
2009 Introduction to Cocoa Development with Xcode
2010 Getting started with Xcode 4
2008 Multicore, Blocks, and Grand Central Dispatch
2007 Cocoa Drawing Techniques
2007 Bringing your Java App to the Mac
2008 Building Great Java Apps