There are several very good references to Perl available. The first and foremost is the Perl manual page. It is about 90 pages long and describes all aspects of Perl, albeit in a terse manner. For me, it is the reference of first resort since I can scan through it in an Emacs buffer.
The book Programming Perl by Perl author Larry Wall and Randal Schwartz is the definitive compendium of all things Perl. It is known colloquially as ``the Camel book'' due to O'Reilly and Associates' habit of putting animals on the covers of their books, in the case a camel. It should be noted, however, that it is not the best book to buy for learning Perl from scratch simply because it is so big. It is a better book to read once you know the basics.
There is a book due out sometime this fall by Randal Schwartz called Learning Perl. It is being written presumably in response to the difficulty of learning Perl from the Programming Perl book.
There is a Usenet newsgroup devoted to the Perl language called comp.lang.perl. This is a forum for discussing nuances of Perl and asking questions about the language. New Perl programmers are encouraged to read the manual pages and the Perl FAQ (mentioned below) and to consult experienced local Perl programmers before posting to the group.