* Learning Perl (like phranque mentioned) - [oreilly.com...]
* Perl Best Practices - [oreilly.com...]
* Perl Testing: A Developer's Notebook - [oreilly.com...]
And if you join a local Perl Monger group, you can get a 35% discount on the books.
Also, the Yet Another Perl Conference, North America (YAPC::NA) is coming up in June. [yapc.org...]
I learned mainly from Programming Perl, which is very comprehensive, but encourages a lot of "perlish" practices that should be avoided. These bad practices are common in most other Perl books.
PerlBP carefully explains the problems with many of the normal way of doing things in Perl. The section on object oriented programming in Perl is particularly good, advocating a completely different model than the most common "blessed hash" method.