ADC Member Site: log in to your ADC account here. Download Xcode and get SDKs and doc updates. You need an account but you can get one for free.
Apple Mailing Lists: Apple maintains a large number of mailing lists on many different subjects. Subscribe to one or just browse through the archives here.
CocoaDev: a wiki for Cocoa development. When you can't find what you need in Apple's docs, look here.
Cocoabuilder: a nicer archive of Apple's cocoa-dev and xcode-users mailing lists.
Cocoa Dev Central: learn Cocoa. Tutorials, guides, blogs, and links.
