Debian includes too many IRC tools to list. You can find them at the following places:
Debian stable.
Debian unstable (didn't receive so much testing).
Also be sure to check the proposed updates. It may have IRC clients as well.
Debian non-free (applications with a restrictive license) contains cIRCus.
RedHat 7.0 includes the following clients:
KSirc from KDE Network 1.1.2.
Slackware 7.1 includes the following clients:
KSirc from KDE Network 1.1.2.
X-Chat 1.2.1. Later updated to 1.5.7.