ZNC

ZNC is an advanced, feature-rich IRC bouncer. It supports multiple users, multiple clients connecting to a user, SSL, buffering, and is extensible through the use of modules in C++, Perl, and TCL. It also has an integrated web administration interface to manage the configuration of the server.

Install the package:
pacman -Sy znc

Create a user to run ZNC. Default values are fine, since this won't be a used by anyone but the daemon.
adduser znc

Then, you may want to remove the password on the account so no one can log in to it (additional security).
passwd -d znc

Configuration
Edit /etc/hosts.allow and add this line, using the port you will specify in the configuration later. By default this is 6667. If you want to restrict to just your network or a specific IP, change "ALL" to either a netmask in CIDR notation or an IP address.
6667: ALL

Next, switch to the ZNC user.
su - znc

Now, run the ZNC configuration program to generate the required config files.
znc --makeconf

Follow the steps to create new users, configure the users, add networks to connect to, etc. Remember you can easily modify all of these values from the web interface afterward. Be sure to flag at least one user as an admin so you can manage global configuration from the web interface.

ZNC will start after configuration has finished. The default port for the server and web administration is 6667.
At this point you can connect to http://your.plugs.ip.addr:6667 and manage users and global configuration. You can now use your favorite IRC client to connect to the server using the same port.

Start at Boot
Since ZNC will be running as another user, the easiest way to do this is to set up a cron entry to start at reboot. This example also shows setting the EDITOR environment variable to change the editor used to nano. Default is vi if it isn't specified.
su - znc EDITOR=nano crontab -e

In the editor, add this line:
@reboot znc > /dev/null 2>&1

Save and exit, and the entry is now installed.