My Mac OS X instant messaging (IM) client is Adium … it is a pretty good replacement of Trillian on Windows.  But I just learned it does not do IRC.

So I turned to my Friends In Tech and found the following recommendations:

• Colloquy (Victor)
• Conversation (Chuck)
• Ircle (Douglas)
• X-Chat Aqua (Douglas)
• Fire (George)

I am trying out the Colloquy one right now.  It seems to be just the right thing for me.

Also Kreg pointed me to this great resource: opensourcemac.org.