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http://en.wikipedia.org/wiki/Comparison_of_Internet_Relay_Chat_clients

Is a nice helpful list.

mIRC was and probably still is one of the most popular irc client despite being a payware.
I've known people use hydra, xchat / hexchat, chatzilla and so on.
Andchat or Colloquy on Android / iOS.
Personally I use KVIrc.

As for the channel names, all channel names come with the # sign infront. No it doesn't mean hash tag...

So to enter a non passworded channel it'd be /join #randomchannelhere

As for the irc server / channel, the link given by AZD. The first part up to the .net is the irc server, the latter half is the channel name.