Links

Mac OS X Reversing Blog:
Yet Another Reverse Engineering Blog
POP/POP/RET (RE:Trace) Blog
Reverse.put.as

OS X Reversing Related Articles:
The 0xf001's OSX Reversing Section (dead)
Phrack : PowerPC Cracking on OSX with GDB
Phrack : OS X heap exploitation techniques (PPC)
ToxicSoftware's AquaticPrime Warning and AquaticPrime Aftermath
A Brief Tutorial on Reverse Engineering OS X
WikiBooks Reverse Engineering / MacOS X
Cracking Software on the Mac


OS X Hacks:
CocoaDev Page about Input Managers
CocoaReverseEngineering


Debugging (GDB):
Debugging Assembler on Max OS X : Intro to gdb binary debugging.
Cracking Software on the Mac (GDB Cheat Sheet)
Debugging iTunes and other "non-debug" Apps in GDB.
Apple Technical Note TN2032 - Getting Started with GDB
Apple Technical Note TN2124 - Mac OS X Debugging Magic
Debugging with GDB - Richard Stallman, Roland Pesch, Stan Shebs, et al.
GDB Internals
Apple Technical Q&A QA1388 - Symbol to Library in GDB
Apple Technical Q&A QA1361 - Detecting the Debugger
Apple Technical Q&A QA1279 - Remote or Two-Machine Debugging Applications with GDB

Objective-C / Cocoa / OS X Architecture
Inside the Objective-C Runtime Part One and Part Two
GNU Libtool
Mac OS X ABI Dynamic Loader Reference


Assembly:
Intel assembler on Max OS X Small intro to Assembler under Mac OS X (x86).
The Netwide Assembler: NASM - Apple Document for OS X Intel
Apple Introduction to Mac OS X Assembler Guide
PowerPC Assembly Tutorial

Apple's Developers Docs:
Apple Developer Connection Site

OS X Reversers:
McScribble's Blog and his Disassembler project post

Anti Cracking/Debugging, Discussion about Protection:
Unsanity's Pirate-Me-Not Article
CocoaDev CocoaInsecurity
CocoaDev SoftwareSerializationPiracyDiscussion
Five Reasons To Ignore John Gruber’s OS X Security Punditry
Apple Technical Q&A QA1361 - Detecting the Debugger

Further Readings
Exploring Protocols Part 1 and Part 2
Infecting Mach-O Files
Understanding Apple's Binary Protection in Mac OS X from Mac OS X Internals Book, Bonus Chapter
Breaking Mac OS X and Mach-O Infection
Understanding admin to root privilege escalation in Mac OS X and nice Links
Abusing OS X

Related Blogs
Ilfak's HexBlog
Matasano Chargen, his reversing articles and his development ones

Tools
Class-Dump Project Page and the Author's blog and the CocoaDev Page
Code-Dump Project Page (PPC)
Lua Script OTX output -> IDC -> IDA Enhanced disassembly

Misc
Various Mac OS Reversing Text & Tools
Mac Software Security Links