IRC Clients

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.