Irssi is a fabulous IRC client, which runs on the command line. I'm sure I don't use half the features it offers but its very stable, unintrusive ( you can run it in a background terminal, or even leave it running in a detached screen process ), and frankly excellent. Because I don't have to set up irssi very often, I always have to look up how to do it - here's the quick start guide (and remember you can use any of the commands with a "help" argument to get instructions)

First of all, we create a network

/network add -nick  -user

/network add -nick fred -user fred freenode

Next up, we add a server to the network - this step is so we can add a number of alternative servers for the same network, I never do though.

/server add -noauto -network

/server add -noauto -network freenode irc.freenode.net

You can also use -auto rather than -noauto above to reconnect to this network every time you use irssi.

Finally, we connect.

/connect

/connect freenode