Macintosh: Most Applications Crash; If Not, The Operating System Hangs. (Note: That sentence is neither mine nor meant serious nor correct. Just playing with words:-)

• Apple documentation: Intro to Mac Programming (extensive documentation, source code & development tools); Developer Documentation; Technical Documentation (FTP); What's new
• Apple indices: Function Index und Technology Index
• Mac OS Developer World from Apple
• Knowledge Base
• Mac C Tutorial
• Mac Pascal tutorial
• Mac Programming FAQ
• Gestalt selectors
• International Glossaries - information about standard translations of certain notions in user interfaces of Mac software
• File formats (quite complete): wotsit.org; fileformat.info/
• Graphics file formats (specifications): ora.com; NCSA
• Internet protocols: NCSA; W3C (World Wide Web Consortium); HTTP (W3C)

• Sample source code from Apple
• Darwin - Apple's Public source code of Mac OS X
• Devinfo - developer information
• info-mac.org (RWTH mirror)
• HyperArchive
• Nanosaur (complete 3D game!)
• Mactech (FTP)
• W3C Sample Code Library (Internet applications)
• Witness of Teachtext (Uli's World WDEF et al.)
• merzwaren.com
• Braun's C/C++ Junkyard
• Metamage - tools for wizards

• SDKs - Software Development Kits and the most recent Universal Interfaces
• Apple Development Tools
• Mozilla Directory: development links
• MacsBug; MacsBug Basics - introduction to Apple's debugger; "Develop" articles about debugging
• PowerPC assembler programming: complete reference
• Find it in Apple Technical Publications
• "Develop" articles (sorted by topic)
• Mercutio MDEF - dynamic menus
• MIT Information Systems
• Everything Macintosh
• Macinsearch Programmer's Link Library
• program.com - not targeted at Mac developers, but useful algorithms (e.g. chess, presentation of animated GIFs)
• Ultimate Macintosh
• AppleScript
• Hints for designing and implementing good user interfaces: Human Interface Subtleties; Making Information Usable
• Background-Only Applications (Technote 1070)
• CGI programming: Grant's CGI framework; CGI Resources (several, not especially for Macs); NCSA (ditto); Websiphon
• Version control systems
• Random-number generator
• Programming of contextual menu extensions
• HTML 4
• Associated Mac User Group
• Debugging tools (mainly about memory management): QC/Spotlight; Heap Manager (also source code available!)
• C programming (not Mac-related); C course; FAQ; miningco.com
• A/UX FAQ