As you said in Private Message, there is Snak. Snak is not only for Mac OS X as you said though, as it says on its
requirements page,
"Snak requires MacOS version 9 or newer. Snak is fully compatible with OS X".
You actually cross posted in a thread which listed other Mac clients. Also, if you looked in the thread I linked to above, and followed the links there, other IRC clients are mentioned.
IRCle is another one for the Mac.
Regards,
