/msg <nick> <msg>
/query <nick>
/ctcp <nick> <ctcp...>
/ping <nick>
/ctcpreply <nick> <ctcp>
/me <msg>
/clear

/topic <topic>
/names
/kick <user> <reason>
/mode <modes...>

/dbgserver
/dbgchan
/dbgdns <host>
/dbgplugins

Change user modes. DO NOT specify your nick.
Send a message
Open a query window with <nick>
Send a CTCP <ctcp> to <nick> (do not use for pings)
CTCP Ping 
Send a CTCP <ctcp> reply to <nick>
Do an action in a channel or query
Clear the current window

Changes topic.
Show who's on channel.
Kick <user> for <reason>
Change channel modes

Show information about currently connected server
Show information about current channel
Perform a DNS lookup on <host>. Forward only, no reverse.
List currently active plugins