Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Gajim - Full featured and easy to use Jabber client
irssi - Irssi is a terminal based IRC client for UNIX systems.
Empathy - Apps/Empathy - GNOME Wiki!
Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.