irssi http://www.irssi.org/

Indeed, irssi is the only acceptable choice.

Combined with Screen. I suppose that goes without saying.

Truly, it is the only way to roll! I run IRSSI on my server, allowing my to stay perpetually connected. Additionally, I can join from any device that supports SSH! It's a great solution, even if it's a bit hard to get used to at first.

I've found it vastly more convenient to run ZNC (or the like) on the server and use irssi locally. Otherwise I typically have to fight with key bindings and finicky settings on each machine (some of which I can't change). This also lets you use any number of clients.

For example, I'm running irssi on my laptop, colloquy on my iPhone, and a few scripts which handle pushing notifications, all from the same connection.

I've always used screen, but may switch to a bouncer next, mainly to get better support on mobile, and the ability to route notifications. It does seem like a more elegant solution.

You should check out WeeChat as it's a modern and actively updated terminal-based IRC client. Irssi is definitely not the only acceptable choice.

If you want a GUI I'd recommend Konversation (if kdelibs is OK). There's a Qt-only client called Quassel as well (which also supports a UI/core separation so you can close the program and remain logged in)

weechat: http://www.weechat.org/

ERC, if you're an Emacs user.