colloquy.png Colloquy is an open source MacOSX IRC client. As with most MacOSX applications, this one is pretty, clean, and easy to use. It also has clients for the iPhone and iTouch.
Need a buddy list for your IRC buds? No problem. There is one. Full DCC transport? No problem. A way to chat on multiple servers at once? YAH! It has everything you need for IRC and more.