In addition to the excellent free resources mentioned above, there will also soon be:

Perl Best Practices, by Damian Conway, O'Reilly, August 2005, 550pp, ISBN: 0-59600-173-8

which offers a comprehensive coding standard (256 guidelines).

I'll leave it to my fellow monks, several of whom have helped me fine-tune the book, to tell you whether or not it will be worth waiting two months, and then paying good money, for. ;-)