Till, Teach Yourself PERL in 21 Days, SAMS Publishing, 1996. Excellent instructional text and reference manual.
Schwartz, Learning Perl, O'Reilly & Associates (http://www.ora.com/), 1994. A good starting point.
Wall and Schwartz, Programming Perl, O'Reilly & Associates, 1992. A good reference, but doesn't cover PERL 5.
Wall, Christiansen and Schwartz, Programming Perl (2nd Edition),
O'Reilly & Associates,
1996. A good reference, covers PERL 5.