If you are planning to use Perl seriously, I would recommend O'Reilly's Perl books. O'Reilly is the leading publisher on Perl. For practical programming books on any language, they are hard to beat.
Here is their Perl page: http://www.oreilly.com/pub/topic/perl
Beginning
- Learning Perl, Fourth Edition (2005)
There is a Windows edition that is quite old (1997). It is not recommended because modern Windows and Unix are not that different for the purposes of linguistic code.
Intermediate
- Intermediate Perl
- Perl Cookbook (useful for ideas on how to do a particular task)
- Mastering Regular Expressions (useful for any programming language, not just Perl)
Reference
- Programming Perl, also known as the Camel Book.
Non-Computational Linguist
In case you are recommending a book for linguists who are just curious about programming, Michael Hammond's "Programming for Linguists" seems useful. It starts off pretty slowly and doesn't cover anything in depth, but it appears to have good coverage over all.
See also: