Create the list  of items  to appear in the dropdown list in a range (could be on
another sheet.) Select all the cells  in the range, then assign the range a name
(Insert >> Name >> Define). Assume you named the range TheList. Select the first
cell which should display the list as a dropdown box. Select Data >> Validation.
On the Settings tab of the Data Validation dialog that appears, select List in
the Allows dropdown box. In the Source textbox, enter =TheList and click OK.
This creates the dropdown based on the named range. You can copy & paste this
cell; wherever you paste it will have the same dropdown list. This also lets you
maintain the list in one place: the named range (TheList).