What follows is a list of excellent online resources to help you learn more about Mac OS X programming and related topics.
• http://www.triplesoft.com/—The Web site for the book you are holding in your hands. This site contains source code projects, updates, and more!
• http://developer.apple.com/—The Apple Developer Connection contains online documentation, sample source code, and development tool updates to help you get the most out of your Mac OS X development efforts.
• http://www.cocoadev.com/—This interactive Web site for Cocoa developers hosted by Steven Frank contains a lot of great information, discussion, and sample code with explanations.
• http://cocoa.mamasam.com/—The CocoaDev and MacOSXDev mailing list archives, which are searchable on the Web. If you are having a problem, odds are that someone has already solved it.
• http://cocoadevcentral.com/—Many useful tutorials for Cocoa newbies.
• http://www.omnigroup.com/—Developer resources, debugging utilities, and frameworks to make your development easier.
• http://www.stepwise.com/—Numerous articles and information for developers.
• http://www.macosxhints.com/—An excellent collection of (mostly) command-line–based hints for Mac OS X. Advanced users are encouraged to explore via the Terminal.
• http://homepage2.nifty.com/hoshi-takanori/cocoa-browser/—Cocoa Browser is a great program by Hoshi Takanori, Max Horn, and Simon Liu that allows simple and fast browsing of the Cocoa API reference documents. If you are a Cocoa programmer, you need this—it's free and is released under the GNU General Public License.