I wanted to second the recommendation for the Perl Cookbook, and to emphasize that it's more than just a bunch of little routines: every one of them is discussed throughly, and gathered together into logical chapters, e.g. the chapter on XML is probably the first thing you should read on the subject of perl and XML.

But I also wanted to say, don't neglect the on-line documentation. Perl comes with a very complete set of reference information, and also quite a few tutorials on different subjects. If you do a "man perl", you'll see a listing of other perl man pages, and right at the top is a section on the tutorials, including subjects like references, data structures, regular expressions and objects...

And once you're through that material, you might try looking at the Perl Design Patterns site.