This is a meta-answer, but the Perl Tips archives contain all sorts of interesting tricks that can be done with Perl. The archive of previous tips is on-line for browsing, and can be subscribed to via mailing list or atom feed.
Some of my favourite tips include building executables with PAR, using autodie to throw exceptions automatically, and the use of the switch and smart-match constructs in Perl 5.10.
Disclosure: I'm one of the authors and maintainers of Perl Tips, so I obviously think very highly of them. ;)
