irssi - Irssi is a terminal based IRC client for UNIX systems.
Gajim - Full featured and easy to use Jabber client
WeeChat - WeeChat is a fast, light and extensible chat client.
CoyIM - CoyIM is a safe and secure chat client.
KVIrc - KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit.
Empathy - Apps/Empathy - GNOME Wiki!