IrcClient-csharp

Current events:

UserJoined - fires when a user joins
UserLeft - fires when a user quits
ChannelMessage - fires when a channel message is received
PrivateMessage - fires when a private message is received
NoticeMessage - fires when a notice is received
UpdateUserList - fires when the IRC numeric 353 is received (user list)
NickTaken - fires if the client's nick is in use already
Disconnected - fires when the client is disconnected (currently disabled)
OnConnected- fires when the client is connected (when you are able to join a channel)
NickChanged- fires if someone changes their nick
ExceptionThrown- fires when an exception is thrown on the underlying thread

Example usage:

// new instance
client = new IrcClient("server", 6667);

// connect to the server
client.Connect();

// join channel
client.JoinChannel("#channel");

//send message
client.SendMessage("#channel","Message");

//send notice
client.SendNotice("user","Message");

//listen for channel messages
irc.ChannelMessage += (o,e) =>
{
    rtbOutput.AppendText(e.User + ":\t" + e.Message + "\n");
    rtbOutput.ScrollToCaret();
};