Linkinus Linkinus is an advanced, easy-to-use IRC client for Mac OS X that is growing rapidly in popularity for it's great user interface as well as its many features. Shareware.
X-Chat Aqua is a Mac OS X IRC client. If you are familiar with XChat for UNIX/GTK+/X Windows, then you will be at home with X-Chat Aqua. Free.
Traditionally, chat clients on the Mac have been anything but glamorous. Colloquy is an advanced IRC & SILC client which aims to fill this void. By adhering to Mac OS X interface conventions, Colloquy has the look and feel of a quality Mac application. Free.
IRC for the rest of us. Conversation makes chatting on the IRC network as easy as using iChat. Conversation allows you to chat in channels and with your friends in a simple, elegant and iChat-like interface without the use of any text command. Free.
With Snak you can participate in conversations in Internet Relay Chat (IRC) channels. IRC channels are like meeting rooms on the Internet, where people from all over the world can meet and chat. Shareware.
Xirc is an internet relay chat application written in Cocoa-Objective-C for Mac OS X (10.3 & 10.4 Universal) It is fully customizable and scriptable via AppleScript, Perl or using the powerfull 'C' internal scripting language. Shareware.
Ircle allows you to connect to up to 10 networks at the same time. Each connection can have 10 channels. With Quicktime and a camera or microphone installed you can even send live audio and video to other ircle users. An SSL compliant version is due out soon. Shareware.
mIRC is a client for the Windows platform which has extensive capibilites to connect many networks at once, and is reguarded as the best client on the Windows platform.