Xchat is possibly one of the best IRC clients ever made. It is more user friendly and cleaner than mIRC. Unlike HydraIRC, this client is a finished product with no loose ends. Plus, it is an open-sourced project so there will always be future updates.
Of course, there is an xchat 2 in development by silverex at http://www.silverex.org/faq/
Sunfizz 