I have to agree with some of the other responses - Perl's POD is a good first step, but it's inadequate for larger projects. I've recently worked on a project that involved C++, and we decided to try Doxygen for our API documentation. I have to say, I am very impressed with it - it can generated interlinked HTML documentation (ala Javadoc), tex output (with the ability to produce a PDF manual), and manpages. It has facilities for documenting at the class level, member level, as well as parameters and return values from methods. It generates class hierarchies.

It is my opinion that Perl would be well served by adopting a documentation tool/format with a similar level of features. The links really help developers get familliar with the project quickly, the generated hierarchy diargrams and collobration diagrams really aid in understanding object hierarchies.

There has been some talk about this for Perl6

Kyle