IRCle is often recognized as the defacto standard for IRC on the Mac. It is flexible, powerful, and fully featured. It is probably the most popular IRC client for the Macintosh. IRCle also has a notoriously steep learning curve with its complicated interface and menus.

There are are plenty of good IRCle configuration pages that go into a lot more detail than this one. This page is primarily set up to simply get you up and running, if you have any questions beyond that, you should check out those other ones (some listed at the bottom of this page).