Cores
Advanced - Beyond the Apple GUI and typical usage
General
- Mac OS X Hints.com
- Daily tips and tricks for improving your Mac experience, both in the GUI and terminal.
- TinkerTool
- Just like it sounds, this app will provide you access to the many optional settings that your OS has disabled by default.
Web Resources
- Maintain.se - Blog
- Brought you by the gang that makes that great maintenance tool, Cocktail, this site is full of great hidden OS X enhancements.