This is a list of current IRC clients available in Debian (either in Stable/Testing/Unstable). It does not attempt to compare these clients. We just give the list in alphabetical order. Try a few and decide which one you like best. Please add to the list if your favorite IRC client is not here.
empathy - requires GTK
erc - IRC within GNU Emacs
Irssi - text mode
konversation - requires KDE
kopete - requires KDE
ksirc - requires KDE
pidgin - supports multiple protocols, plugin system
if "Waiting for network connection" try "pidgin -f"
quassel - distributed IRC client
Smuxi - requires GTK
WeeChat - text mode
XChat - requires GTK
Web based IRC client
Web based www-to-irc gateways are useful if you're behind a firewall that blocks irc traffic (or if you don't want to install an IRC client software):
http://www.mibbit.com/chat/ (supports https).
For a client comparison, please see Wikipedia's comparison of IRC clients.