TSQL
sp_passsword -> Changes password for a specific login name.
e.g. EXEC sp_password ‘oldpass’, ‘newpass’, ‘username’
sp_tables -> Shows all the tables in the current database.
e.g. EXEC sp_tables
xp_cmdshell -> Runs arbitary command on the machine with administrator privileges. (most imp)
xp_msver -> Shows the MS SQL server version including the all info about the OS.
e.g. master..xp_msver
xp_regdeletekey -> Deletes a registry key.
xp_regdeletevalue ->Delets a registry value
xp_regread -> Reads a registry value
xp_regwrite -> Writes a registry key.
xp_terminate_process -> Stops a process