A few days ago, I released Const::Exporter to CPAN.
Basically, it's a module that allows you to define a module with exportable constants that:
- can be read-only scalars, arrays, or hashes (as well as the standard constant functions);
- can refer to each other;
- can be grouped into export tags, and added to multiple tags without repeating the value;
- and easily interspersed with POD describing the constants.
A more detailed discussion of it is on my blog