There are thousands of different IRC channels, on every subject under the sun. For example, a few of the well known, popular IRC channels are listed below.
One of the best way to find channels you are interested in on a specific network once you are logged in is with the list command.
You can also find channels by geographic location. There are many IRC channels established for people from various cities, although of course anyone in the world may join them. For example, the channels #toronto and #new-york are often full of people from those cities as well as various virtual tourists.
You can also consult indexes on the web. The following sites maintain lists of IRC channels: