QuIRC is a stable and powerful IRC client. It features a clean interface that scales well to many servers and channels. It includes many features that power users will appreciate. It contains advanced scripting facilities powered by Tcl, accompanied by Tk. It has been called by some what XiRCON should have been, and by others, simply great.
savIRC is a graphical IRC Client that supports multiple connections and many popular IRC client features as SOCK5, ctcp, dcc, ignore and notify lists, mIRC colors , URL caption, nick completion, dedicated windows.
tkirc2 is a freely distributable graphical user interface for the Internet Relay Chat (short: IRC). It uses the text-based client ircII as backend to the IRC and offers some nice extensions.
Zircon is an X Window System interface to Internet Relay Chat. The software is written in tcl/tk and uses the native network communications of tcl. Zircon has more features than you could possibly imagine and implements nearly everything that the irc II clients support.