Which code to read?
Peter Seibel has written a great blog post on code reading - learning more about programming by reading good examples. The final model he describes has someone diving into a piece of code like a 19th century explorer and then reporting back to the group on what they found. This sounds like a valuable activity for a Perl Mongers group.
So my question to you is what CPAN module would you recommend as rewarding to an intrepid code explorer; and why? Of course I'm not suggesting Perl programmers should only read Perl code, but I do think CPAN is a good place to start.