MacIndie

NSLog is not just useful for printing out your variables in the heat of a debugging session – for instance, did you know you can get NSLog to spill the beans on the line number you’re on in the current method, or the path of the current file?  There are a number of compile-time macros [...]

URL: http://code.google.com/p/plcrashreporter/
Code Quality: Production (used in many OSX and iPhone apps)
Description:
PLCrashReporter is an Objective-C framework (on MacOSX) and a static library (on iPhoneOS) that allows you to capture application crash dumps and send them back to yourself for analysis. PLCrashReporter is implemented as an in-process signal handler that can handle both fatal errors (segmentation faults, [...]

URL: http://code.google.com/p/google-toolbox-for-mac/
The Google toolbox for Mac is a collection of open source code for the Mac and iPhone. It includes several different modules including:

Objective-C Address book API for iPhone.
A large number of Foundation and AppKit extensions and categories
Debugging utilities
Spotlight importers useful for developers
A complete and extremely capable unit testing harness
A set of XCode configs useful [...]