Any IRC client will work, but here is a short list of clients which are recommended.
|Weechat||Multi-platform command line IRC client|
|silverex||SilverX is similar to XChat, but its free for windows|
|AdiIRC||AdiIRC free client(Windows) with great plugin support, clean and powerful|
|XChat||Cross-platform GUI client|
|Textual||Mac OS X Client|
|Palaver||iOS IRC Client (probably the best, integrates with ZNC)|
|Colloquy||Mac OS X, iPhone and iPad client|
|irssi||Multi-platform command line client|
You can find a Comparison of IRC clients on Wikipedia.