HexChat - HexChat is a fork of XChat with bug fixes and new features.
mIRC - mIRC: Internet Relay Chat client
Pidgin - Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.
irssi - Irssi is a terminal based IRC client for UNIX systems.
KVIrc - KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit.
WeeChat - WeeChat is a fast, light and extensible chat client.