Some books I have found useful:

Perl:

• Perl Best Practices.
• Effective Perl Programming (a.k.a. the Shiny Ball book).
• Network Programming with Perl.
• Mastering Perl/Tk.

System Administration:

• Essential System Adminsitration.
• TCP/IP Network Administration.

If I did a lot more programming I would pick up "Higher Order Perl" as well. And "Code Complete" and "Rapid Develpment" are good general purpose books.