There are instructions how to do this via Xterm so that a "reboot" option appears in the dropdown menu on the on/off button but they seemed so long winded to me I have never bother trying them out.

I agree an app we could download for us noob's would be a great option.

PS Beaten to the answer by a minute however this bit always put me off

"6) Create a backup copy of the systemui file by typing cp systemui.xml systemui.xml.bak (if things mess up i dont know how to use this backup to repair things)"

Not much point of making a backup if I didn't have a clue what to do with it if things went wrong??