Doxygen
For those of you who don’t know, doxygen is a mature system for creating documentation of your source code. Which can be downloaded from the doxygen website here. This is a really useful and intuative system, particularly for large projects that produces a variety of output and styles.
With it you can produce output as HTML, LateX or a few other common formats. On the website is a .dmg file which makes it incredabley easy to use - i am amazed its not more well publicised on the mac to be honest!