bersIRC (http://www.bersirc.com) is a wickedly cool IRC client, currently available only for Windows, but with a Linux version in development.
bersIRC was primarily written to "fill the gap" left by other IRC clients, and has support for multiple server connections, plugins and a powerful scripting language based off of Object Pascal/Delphi.
It is written using Delphi 5, and the official channel for it is #bersirc on EFNet.