OTRS (Open Ticket Request System) is a great open source ticketing system with a pretty clean interface, written entirely in Perl. Below are some notes from setting this up on Centos 5.5, see the website above for full install instructions.
some things to remember:
run /opt/otrs/bin/otrs.checkModules to verify that everything is installed correctly, RPMForge yum repo can help with Perl packages
use generic agent to automagically move tickets/delete tickets. This works great for deleting stuff in the junk folder.
set up 2.4.9, not 3.0 (the interface was significantly changed in 3.0, not used to it yet. I think there was another reason for this as well, but I can't remember this right now).
remember to set up mysqld and httpd with chkconfig --levels 2345 <daemon> on