IRC Clients for Windows
Most users on Windows choose to use the popular shareware client, mIRC, which is available for a 30 day trial, and costs $20.00 after the trial period.
XChat and derivatives
The popular Unix IRC client XChat and a number clients forked from it are also available for Windows.
ChatZilla is a viable choice for Windows users, and a particularly compelling one for users who regularly switch between different platforms.
Instant Messaging programs
Trillian, Miranda, Pidgin, and other “all in one” instant messaging programs include IRC as one of their supported protocols.
Bersirc is another choice for Windows users.