mIRC is a highly configurable IRC client. It contains all the goodies other clients on UNIX, Macintosh, and even on Windows offer, combined with a nice and clean user interface. It offers full color text lines, DCC File Send and Get capabilities, programmable aliases, a remote commands and events handler, place sensitive popup menus, a great Switchbar, World Wide Web and sound support, and a lot more. It is shareware, but is not crippled in any way.
Download:
mIRC 6.17 | Mirror | Release Notes