Empathy - Apps/Empathy - GNOME Wiki!
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.
irssi - Irssi is a terminal based IRC client for UNIX systems.
Gajim - Full featured and easy to use Jabber client
mIRC - mIRC: Internet Relay Chat client