Perl Hashes (a.k.a Associative Arrays or Maps)
Introduction
Hashes (also known as "associative arrays", or in other languages as "maps" or "dictionaries") allow the programmer to map arbitrary strings to arbitrary values. Perl has a convenient syntax to support hashes as first order data structures.
Tutorials
The Hash Cookbook
This is a presentation (in OpenDocument format) about hashes by "Jerusalem Perl Monger" that was given by her at the Israeli Perl Workshop of 2007 . It covers the main uses for hashes, with many code excerpts.
Modern Perl (the Book)
Chapter 3 of Modern Perl discusses hashes.
Beginning Perl
Chapter 3 of "Beginning Perl" discusses hashes.
Perl for Perl Newbies Series
The second talk in the series discusses hashes.