Apple Developer Connection: Mac OS X: Apple's developer resource for Mac OS X. Contains guidelines, tutorials and API information for new OS X developers. Most documentation is available in HTML or PDF format

Internet Config: home page for the standard internet configuration AP

Quinn's Human Interface Subtleties: Discusses the sometimes subtle differences between a good user interface and a terrible one. From the author of Internet Config

Resorcerer: Resource editor for Macintosh and MacOS-compatible computers. Includes a template system for easy editing of common resource types, and support for most development environments