Colloquy
It has been awhile since I have used any chat services -- catching up brings some new discoveries...
Colloquy is an advanced client for IRC, SILC & ICB. (I never even heard of SILC.) I think it was the early days of TalkCity was the last time I used an IRC client.
Coloquy has the feel of a Mac OS X applications. It also supports many Apple standards: AppleScript dictionary, plug-ins, customizable, supports full DCC transfers and even has a buddy list. It is also open source.
