Even easier method: hold command and drag it off. It should poof off, just like dragging things off of your dock.
This works with any of the menu bar stuff that comes from the OS. It wont work for third party programs that live in the menu bar though.
Also, the other method given wont work if you dont have MobileMe, as you wont be able to get to the option. The third way to do it would be to open iSync and go to the preferences.