While not the most popular IRC daemon around, it's probably the one which is the most suited for large networks and lower resource usage. Running on a majority of the EFNet servers, ratbox has proven itself as one of the most stable IRCds around. While it doesn't have a number of features found in other IRCds, you can be sure that it will run well even on a moderately powerful server and a few hundred users. Going by size of the configuration file, ratbox has close to 1000 lines which makes it moderately easy to configure. Again, having knowledge about TCP/IP networking and ip-addressing is essential to running your own IRC server.
ircd-ratbox Website.
Inspire IRCD, better known as InspIRCd is the second-to-most popular IRC daemon after Unreal. It owes this popularity to a modular approach. Depending on what modules you install and load, you can add/remove features without the main daemon getting larger and slower. Here is a comparison page given by InspIRCd developers so you can compare the features between them and other IRC daemons.
If you were scared by the large configuration file for UnrealIRCd, InspIRCd is going to scare you even more. A sample configuration file with comments weighs in at a whopping 2300 lines. Add extra configuration to that and you're looking at close to 2500 lines of configuration. But once configured, InspIRCd is a tamed beast which can help your IRC network reach great heights. Proof of that is in the fact that UnrealIRCd will be using InspIRCd's codebase to create the new version of their own IRC daemon.
Inspire IRCd (InspIRCd) Website.
While nowhere near an exhaustive list of all the IRCds around, this small list should help you choose one from the most popular daemons available today. To choose between other IRC daemons, check out this page on Wikipedia which compares and lists all the features found in different IRC daemons. Choose one, go to its respective site, and download the archive to check it out. If you have a spare Linux box lying around and you are what most people would call "nerdy," it'll be a lot of fun to configure your own IRC server. And once you're able to configure one of the daemons to run the way you want it, it should be pretty easy trying out other IRCds. If you run a popular website and need a way to attract permanent membership and create new friendships among your users, no better way than to run an IRC server where your visitors can interact and build communities.