Here is a list of popular IRC networks.

Network	Server	Ports
EFnet	irc.phoenix.net	6667
IRCnet	irc.stealth.net	6667
"	irc.aimnet.com	6667
TalkCity	chat.talkcity.com	6667
DALnet	irc.dal.net	6667
SegaIRC	www.sega.com	37568

Now some of you may be confused to what IRC, networks, channels, etc. are... well I will try to explain in the simplest of terms. Please if you don't understand what I'm talking about ask someone else you know... I am so busy I do not have the time to explain in greater detail to every person that emails me. If I do start to recieve large amounts of email I probably will take this part off. I hope this isn't coming across rudely because I do not mean it to.
Well IRC networks are basically a bunch of servers all connecting to each other. TalkCity has 6 servers which are:
chat.talkcity.com
chat2.talkcity.com
chat3.talkcity.com
chat4.talkcity.com
chat5.talkcity.com
chat6.talkcity.com

They all also have different ports that you can connect through. Most common port numbers for IRC servers:
6666
6667
7000

You may hear people to refer to channels ... which are chatrooms on IRC. Channels start with a # sign. Ex: #NoOnes But on my IRC the # is already written into the script so that you don't have to type it in.
Some popular channels are:
Cyberchat Chataway USA ChatLounge