Developer Resources
Apple Developer Connection
If you develop software on or for the Macintosh Operating System or use it for web development this is the place for you!
Darwin OS
Apple's open source projects center around this BSD based operating system which is the basis for Mac OS X.
IDevGames.com
If you are a game developer who creates games for the Mac or are interested in how to do so, this site is for you!
Webmonkey
A great source of reference material for those developing web pages.
The World Wide Web Consortium (W3C)
The W3C is the standards body for the web. All the HTML, CSS and Document Object Model (DOM) specifications and much more are here.
Security
Packet Storm
If network security tools, information and news are what you need, this is a good place to start.
Security Focus
This is an important resource for anyone concerned with network security. Here you will find important mailing lists, news and other information regarding current security issues, trends and defenses.
Snort.org
Snort is a well known open source Network Intrusion Detection System (IDS). The source code, documentation and more can be found here.
Zone-H.org
Zone-H is another good network security site where you will find advisories, example code and more.