If you ever need to search for certain channels that serve say, "mp3" then all you do is type that in and it will list the channels along with the server and also how many users are currently there. It also shows you what is in the channels topic, this usually just shows what the channel is offering. This is quite useful if you don't feel like scrounging through say all of the 400+ networks :)

Check 'em out:
http://irc.netsplit.de/channels/
and
http://www.xgoogle.com