Konversation - Konversation is an IRC client which gives you speedy access to Freenode network's channels...
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.
irssi - Irssi is a terminal based IRC client for UNIX systems.
mIRC - mIRC: Internet Relay Chat client
Adium - Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more.