Of all the GUI IRC clients, I strongly recommend kvirc:
http://www.kvirc.net/At-least on Windows and Linux; I'm not so sure if it is the best for MacOSX.
@Jim, It is important that you:
1. Connect via SSL
2. Register a username.
3. Set 'ENFORCE' for you username (so other people cannot masquerade as you)
3. Authenticate via SASL (kvirc has built-in support for this).
4. Get a IP cloak. (so you don't tell it to everyone, opening yourself to attack).
I'll set the Channel-server to automatically voice you if you are logged in.