I'm starting to spend more time trying to learn the Cocoa development frameworks. For those not familiar with it, Cocoa is a set of software development frameworks based around the Objective-C programming language. There are a number of different frameworks within Cocoa, including GUIs, networking (and IO in general), graphics & imaging, distributed computing, etc.
The most obvious site for learning about Cocoa is the Apple developer website. But, with the help of some friends who are also trying to learn Cocoa, I'm starting to find other good resources on the web for learning Cocoa. Since Cocoa is not as well-known as Java, C++, or Ruby, it's like discovering a whole new world on the web. Here are a few links I'm finding useful:
Cocoa Dev Central - a sort of almanac of Cocoa-related material
Cocoa Blogs - a website listing blogs of people discussing Cocoa (I still need to drill down on this one)
CocoaLab - has a PDF trying to help non-programmers learn how to program Cocoa.
CocoaHeads - "CocoaHeads is a group devoted to discussion of Apple Computer's Cocoa Framework for programming on MacOS X." A sort of clearinghouse for Cocoa Develoer Groups. There's one in St. Louis, so maybe I'll try attending.
IndieHIG - a project to create Human Interface Guidelines (HIG) that are up-to-date with the current Mac OS X look and feel. They feel Apple's guidelines are out-of-date, though the HIG guide on the apple site seems pretty up-to-date to me.
Karelia Software's Cocoa Open Source - "A random collection of useful bits of Cocoa, as found in Watson and in other sundry Karelia applications and testbeds. Feel free to adapt these for use in your Cocoa applications."
Theocacao - a website/blog by Scott Stevenson discussing Cocoa and related topics.
There are even a couple of podcasts on the subject:
Late Night Cocoa
Some of these I found myself, while some of these came from Brian Coyner or David Giovaninni (thanks, guys!).