I've bought a few Perl books besides these, but these are the ones that really helped:

1. Learning Perl -- great intro, best way to start
2. Programming Perl -- learn the more advanced concepts.
3. Effective Perl Programming -- stop coding in PERL, and give Perl a try.
4. Perl Cookbook -- great reference for many common problems.
5. Programming the Perl DBI -- if you're using a database.
6. Ojbect Oriented Perl -- great way to learn about OO in Perl.
7. Perl 5 Pocket Reference -- when you can't remember, look it up.

There are a lot more I want, but have to wait in my large wanted-books queue:

1. Mastering Algorithms with Perl
2. Data Munging with Perl
3. Mastering Regular Expressions
4. Perl for System Administration -- borrowed it
5. Advanced Perl Programming
6. Mastering Perl/Tk
7. CGI Programmming with Perl -- borrowed it
8. Network Programming In Perl -- borrowed it