Last updated September 29, 2011.
joe: thank you.
Prefacing someones username notifies them that someone has responded to them; starting the line with a username (followed by a colon) let's them know that you're 'speaking' to them
/me looks at his watch
Denotes an action, rather than a comment.
/nick joe_p
Changes your username.
/whois joe
Finds more information about another user.
seen joe?
Find out when the last time a user was seen in IRC.
joe^^
"Hey, Joe read above."